Mater Dei High School is a private, Catholic, co-educational secondary school in Santa Ana, California, located in and administered by the Diocese of Orange.

Mater Dei is nationally known for its strong sports programs, especially in football.^[6] It is ranked first in the United States for "best high schools for athletes" by school review company Niche,^[7] and in 2014, Bleacher Report ranked it in the top five high schools in the U.S. for producing professional athletes.^[8] Over 68 percent of the student body participates in some role with a team, in one of the 25 different sports sponsored by the school, which together have won 90 CIF, state, and national championships.^[9]

The Roman Catholic Archdiocese of Los Angeles opened Mater Dei in 1950, the first Catholic high school in Orange County. The school had 111 students and a faculty of seven, including Sisters of Charity of the Blessed Virgin Mary, plus principal Fr. Joseph Eyraud.^[10] In 1953 they were joined by the Patrician Brothers, who taught until 2005.^[11]

Enrollment grew rapidly. The school was originally designed for 800 students, but by 1964, it was serving 1,800.^[12] In the 1970s it became the largest Catholic high school west of Chicago, and overcrowding persisted until 1987, when Santa Margarita Catholic High School, opened in South Orange County.

In 2000, Mater Dei embarked on a major capital campaign to fund a new parking lot, chapel, library, and service buildings, as well as a spate of athletic facilities and in 2019, a much-needed parking garage.^[10]

The school has received mixed attention in local media due in part to their method of scouting athletes from public high schools in due process of offering scholarships as a part of recruitment for their acclaimed football program.^[13][14][15]

In 2021, a lawsuit was filed alleging that systemic hazing pervaded the football program resulting in a "brutal locker room altercation."^[6][16] Another 2021 lawsuit alleged that two Mater Dei football players severely injured a classmate in an orchestrated attack.^[17] Orange County bishop Kevin Vann responded with a public statement supporting the school's leadership and criticizing the "media frenzy".^[18] The school announced it would commission an independent investigation into the allegations.^[19]

In January 2022, a female alumna of Mater Dei filed a lawsuit following the surfacing accusations of hazing, alleging that she was sexually assaulted by a former football coach during the late 1980s.^[20]

Mater Dei High School's teams named the Monarchs, and their colors are red and grey. As of 2023, the school sponsors boys' and girls' teams at multiple levels in 25 sports in the Trinity League, part of CIF Southern Section:

• Baseball
• Basketball
• Beach Volleyball
• Cheerleading
• Cross-Country
• Football
• Golf
• Lacrosse
• Soccer
• Sailing
• Softball
• Swimming & Diving
• Tennis
• Track & Field
• Volleyball
• Water Polo
• Wrestling

In addition, boys' beach volleyball, e-sports, equestrian, ice hockey, and surfing are offered on a club level.^[21]

Known for their football and basketball programs, Mater Dei has also graduated professional athletes Robbie Rogers (soccer), Tiki Ghosn (mixed martial arts), and Greg Woepse (pole vault), as well as ten Olympians.^[22] A total of 15 players have been named Gatorade California State Players of the Year.^[23]