Glenbrook South is a member of the Central Suburban League. GBS is also a member of the Illinois High School Association (IHSA), the organization which sponsors most sports and activities in Illinois.
GBS sponsors interscholastic teams for young and men and women in basketball, cross country, golf, gymnastics, soccer, swimming & diving, tennis, track & field, volleyball, and water polo. Men may compete in baseball, football, and wrestling. Women may compete in badminton and softball. While not sponsored by the IHSA, the school also sponsors teams for men and women in lacrosse, in addition to a women’s field hockey team.
The following teams have finished in the top four of their respective IHSA sponsored state championship tournament:
* Basketball (girls): State Champions (1993–94)
* Golf (boys): State Champions (1967–68)
* Gymnastics (boys): 4th place (2004–05, 07–08)
* Gymnastics (girls): 3rd place (1978–79)
* Soccer (girls): 4th place (2009-10)
* Swimming & Diving (boys): 3rd place (2007–08, 08–09); 2nd place (2006–07)
* Swimming & Diving (girls): 4th place (2007–08)
* Tennis (boys): 4th place (1996–97); 3rd place (1995–96, 2004–05); 2nd place (2002–03)
* Volleyball (boys): 3rd place (1995–96); 2nd place (1998–99); State Champions (2002–03)
* Volleyball (girls): 3rd place (2009-10)
* Water Polo (boys): 3rd place (2007–08)