Here are lists of schools which only admit boys, in the United States

• Catholic High School for Boys (Little Rock)

• Cathedral High School (Los Angeles)
• Crespi Carmelite High School (Los Angeles)
• Damien High School (La Verne)
• DBTI (Rosemead)
• Jesuit High School (Sacramento)
• Loyola High School (Los Angeles)
• Salesian High School (Los Angeles)
• Saint Francis High School (La Cañada Flintridge)
• Servite High School (Anaheim)
• St. John Bosco High School (Bellflower)
• St. Michael's Preparatory School (Silverado)
• Verbum Dei High School (Los Angeles)
• YULA Boys High School (Los Angeles)

Bay Area:

• Bellarmine College Preparatory (San Jose)
• Cathedral School for Boys (San Francisco)
• De La Salle High School (Concord)
• Junípero Serra High School (San Mateo)
• Archbishop Riordan High School (San Francisco)
• Stuart Hall for Boys (San Francisco)
• Stuart Hall High School (San Francisco)
• Town School for Boys (San Francisco)

San Diego area:

• St. Augustine High School (San Diego)

• Brunswick School (Greenwich)
• Fairfield College Preparatory School (Fairfield)
• Notre Dame High School (West Haven)
• Xavier High School (Middletown)

• Salesianum School (Wilmington)
• St. Edmond's Academy (Wilmington)

• Gonzaga College High School
• St. Anselm's Abbey School
• St. Albans School

Miami area

• Young Men's Preparatory Academy (Miami)
• Belen Jesuit Preparatory School
• Christopher Columbus High School
• Klurman Mesivta High School for Boys
• Mesifta of Greater Miami
• Yeshiva Toras Chaim / Dr. Abe Chames High School

Tampa/St. Petersburg

• Jesuit High School (Tampa)

• The B.E.S.T. Academy (Atlanta)
• Ivy Preparatory Young Men’s Leadership Academy (Atlanta)
• Benedictine Military School (Savannah)

Pinecrest Academy (Cumming) puts boys and girls in separate classes.

Chicago area

• Urban Prep Academies (Chicago)
• Brother Rice High School (Chicago)
• De La Salle Institute (boys' campus) (Chicago)
• Fasman Yeshiva High School (Skokie)
• Leo Catholic High School (Chicago)
• Marmion Academy (Aurora)
• Mount Carmel High School (Chicago)
• Northridge Preparatory School (Niles)
• Notre Dame College Prep (Niles)
• St. Laurence High School (Burbank)
• St. Patrick High School (Chicago)
• St. Rita of Cascia High School (Chicago)

Became coeducational

• DePaul College Prep (Chicago)
• Hales Franciscan High School (Chicago)
• Holy Trinity High School (Chicago)
• St. Joseph High School (Westchester, Illinois)

Merged

• Cathedral High School (Belleville area/Southern Illinois)
• Joliet Catholic High School (Joliet)
• Roncalli High School (Aurora)
• St. Procopius College and Academy (Lisle/Chicago)
• St. Mel High School (Chicago)

Closed

• Weber High School

Former

• Gibault School for Boys

Louisville

• DeSales High School
• St. Xavier High School
• Trinity High School

Northern Kentucky

• Covington Catholic High School (Park Hills)

Former boys' schools

• Bishop David High School (Louisville; merged with the all-girls' Angela Merici High School in 1984 to form the current Holy Cross High School)
• Flaget High School (Louisville; merged with the all-girls' Loretto High School in 1973 before closing the next year)
• Newport Catholic High School (Newport; merged into the coeducational Newport Central Catholic High School in 1983)

East Baton Rouge Parish

• Catholic High School (Baton Rouge)

New Orleans (Orleans Parish)

• Brother Martin High School (New Orleans)
• Holy Cross School (New Orleans)
• Jesuit High School (New Orleans)
• Archbishop Rummel High School (Metairie)
• Archbishop Shaw High School (Marrero)
• St. Augustine High School (New Orleans)
• St. Paul's School (Covington)
• Christian Brothers School (New Orleans) boys' middle school - The school has a PK-4 coeducational elementary school in both locations, an all girls' 5-7 middle school in the Canal Street Campus, and an all boys' 5-7 middle school in the City Park Campus.^[1]

St. Landry Parish

• Berchmans Academy of the Sacred Heart (Grand Coteau)

Became coeducational

• De La Salle High School (New Orleans; opened 1949; became coed 1992)

Closed

• Miller-McCoy Academy (New Orleans)
• Alcee Fortier High School (New Orleans) (was coeducational for many years)

Baltimore area

• Archbishop Curley High School
• Boys' Latin School of Maryland
• Calvert Hall College High School
• Gilman School
• Loyola Blakefield
• Mount Saint Joseph High School
• St. Paul's School for Boys

Washington, DC area

• DeMatha Catholic High School
• Georgetown Preparatory School
• The Avalon School
• The Heights School
• Landon School
• Mater Dei School

Former boys' schools:

Closed

• Cardinal Gibbons School (Baltimore)

Became coeducational

• Bishop McNamara High School (DC area)
• Tome School for Boys

• Belmont Hill School
• St. Paul's Choir School

Former boys' schools

Became coeducational

• Boston Latin School (in 1972)
• The English High School (in 1972)
• Central Catholic High School (in 1996)
• The Newman School for Boys, now The Newman School

Detroit area

• Douglass Academy for Young Men (Detroit)
• Brother Rice High School (Bloomfield Township)
• De La Salle Collegiate High School (Warren)
• Detroit Catholic Central High School (Novi)
• St. Mary's Preparatory (Orchard Lake Village)
• University of Detroit Jesuit High School and Academy (Detroit)

Closed

• Austin Catholic Preparatory School (Detroit)
• Notre Dame High School (Harper Woods)

• Saint Thomas Academy

• Saint Stanislaus College

• Christian Brothers College High School
• De Smet Jesuit High School
• Rockhurst High School
• St. Louis University High School
• St. John Vianney High School

Former

• Father Flanagan's Boys' Home (Boys Town)

• Cardigan Mountain School

Now coeducational

• Pinkerton Academy

New York City area

• Eagle Academy for Young Men of Newark
• Bergen Catholic High School (Oradell)
• Delbarton School (Morristown)
• Don Bosco Preparatory High School (Don Bosco)
• Neumann Preparatory School (Wayne)
• Oratory Preparatory School (Summit)
• Rav Teitz Mesivta Academy (Elizabeth)
• Saint Benedict's Preparatory School (Newark)
• Saint Joseph Regional High School (Montvale)
• Seton Hall Preparatory School (West Orange)
• Torah Academy of Bergen County (Teaneck)

Philadelphia area/South Jersey

• St. Augustine Preparatory School (Buena Vista Township)

Trenton area

• Christian Brothers Academy (Middletown Township)
• American Boychoir School (Hopewell)

Merged

• Thomas Jefferson High School into Elizabeth High School

in New York City:

Bronx

• Eagle Academy for Young Men of the Bronx
• All Hallows High School
• Cardinal Hayes High School
• Fordham Preparatory School
• Mount Saint Michael Academy
• St. Raymond High School for Boys

Brooklyn

• Eagle Academy for Young Men Ocean Hill/Brownsville
• Excellence Boys Charter School
• Gerer Mesivta Bais Yisroel School
• Mesivta of Seagate School
• Mikdash Melech Mechina School
• Sinai Academy
• Tiferes Academy
• Torah Academy High School
• United Lubavitcher Yeshiva
• Yeshiva Chanoch Lenaar
• Yeshiva Derech HaTorah High School
• Yeshiva Gedolah of Midwood
• Yeshiva Karunas Halev
• Yeshiva Rabbi Chaim Berlin
• Yeshiva Tiferes Yisroel
• Yeshiva Toraf Hesed
• Yeshiva Vyelipol School
• Yeshivat Shaare Torah Boys High School

Manhattan

• Eagle Academy for Young Men of Harlem
• Browning School
• Buckley School
• Collegiate School
• La Salle Academy
• Regis High School
• St. Bernard's School
• Saint Thomas Choir School
• Xavier High School
• Yeshiva University High School for Boys

Queens

• Eagle Academy for Young Men Southeast, Queens
• Cathedral Preparatory School and Seminary
• Holy Cross High School
• Mesivta Ohr Torah School
• Mesivta Yesodei Yeshurun
• Yeshiva Berachel David-Torah School
• Yeshiva Binat Chaim - Boys School
• Yeshiva of Far Rockaway
• Yeshiva Shaar Hatoreh Research

Staten Island

• Eagle Academy for Young Men of Staten Island
• Monsignor Farrell High School
• St. Peter's Boys High School
• Yeshiva of Staten Island

Outside of New York City:

Hudson Valley

• Archbishop Stepinac High School
• Avir Yaakov Boys School
• Iona Preparatory School
• Salesian High School

Long Island

• Chaminade High School

Former boys' schools:

Became coeducational

• Loyola School (Manhattan)
• Monsignor McClancy Memorial High School (Queens)
• New York Military Academy
• St. Francis Preparatory School (Queens)
• Xaverian High School (Brooklyn)

Closed

• Brooklyn Preparatory School
• Rice High School (Manhattan)
• St. Agnes Boys High School (Manhattan)
• St. Nicholas of Tolentine High School (Bronx)

Arden

• Christ School

Columbus

• Saint Charles Preparatory School

Cincinnati area

• Elder High School
• La Salle High School
• Moeller High School
• St. Xavier High School

Cleveland area

• Ginn Academy (Cleveland)
• Benedictine High School
• St. Edward High School
• Saint Ignatius High School (Cleveland)
• University School

Dayton

• Dayton Boys Preparatory Academy

Toledo area

• St. Francis de Sales High School
• St. John's Jesuit High School and Academy

Former boys' schools

• Cathedral Latin School (Cleveland Area) (merged into coeducational school)
• St. Joseph High School (Cleveland area) (merged into coeducational school)

Philadelphia area

• Boys' Latin of Philadelphia Charter School
• Devon Preparatory School
• Father Judge High School
• Holy Ghost Preparatory School
• La Salle College High School
• Malvern Preparatory School
• Monsignor Bonner High School
• Roman Catholic High School
• Saint Joseph's Preparatory School

Pittsburgh area

• Central Catholic High School

Former boys' schools:

Closed

• Northeast Catholic High School (Philadelphia)
• St. James High School for Boys, Chester
• The Young Men's Leadership School at Thomas E. FitzSimons High School (Philadelphia)

Merged

• Monsignor Bonner High School, into Bonner & Prendergast Catholic High School (which initially had separate gender campuses)
• Saint John Neumann High School (Philadelphia) into Saints John Neumann and Maria Goretti Catholic High School
• West Philadelphia Catholic High School for Boys into West Philadelphia Catholic High School

Became coeducational

• Central High School (Philadelphia)
• Milton Hershey School (Derry Township)
• The Hill School (Pottstown)
• Valley Forge Military Academy and College (Radnor Township)
• Cardinal Wuerl North Catholic High School (Pittsburgh)

• Memphis University School
• Presbyterian Day School
• Christian Brothers High School
• St. Dominic School

The McCallie SchoolMontgomery Bell Academy

Dallas-Fort Worth

• Barack Obama Male Leadership Academy (Dallas)
• Cistercian Preparatory School (Irving)
• Jesuit College Preparatory School of Dallas (Dallas)
• St. Mark's School (Dallas)
• Young Men's Leadership Academy at Fred F. Florence Middle School (Dallas)^[2]
• Young Men's Leadership Academy at Kennedy Middle School (Grand Prairie)

El Paso

• Cathedral High School

Houston

• Mickey Leland College Preparatory Academy for Young Men
• The Regis School of the Sacred Heart
• St. Thomas High School
• Strake Jesuit College Preparatory
• The Lawson Academy (formerly William A. Lawson Institute for Peace and Prosperity (WALIPP) - Texas Southern University (TSU) Preparatory Academy) - boys' program^[3]

San Antonio

• Central Catholic Marianist High School

Became coeducational

• Holy Cross of San Antonio (San Antonio)
• Pro-Vision Academy
• St. Anthony Catholic High School (San Antonio)

• Woodberry Forest School
• St. Christopher's School

King Abdullah Academy is coeducational but has separate boys' secondary classes.

Collegiate School is coeducational but puts boys and girls in separate classes during the Middle School years.

Became coeducational:

• Bishop Ireton High School

• Annie Wright Schools has a separate boys' high school
• O'Dea High School

• Father Dueñas Memorial School

Note that some juvenile correctional facilities are named as "Boys' School" or "School for Boys", such as:

Closed

• Florida School for Boys (Arthur Dozier)
• Gatesville State School for Boys

• List of girls' schools in the United States