Objective: To explore the use of physical and mental health services for adolescents who are enrolled in managed care and have access to a school-based health center (SBHC), compared with adolescents enrolled in managed care without access to an SBHC. Design: Retrospective cohort designed with age, sex, and socioeconomic status matching to compare the use of health services for adolescent members of Kaiser Permanente of Colorado (who had access to SBHCs) with those with no access. Participants: The study included 342 adolescents, resulting in 3394 visits that occurred during 3 academic years. During the study, 240 adolescents with access to an SBHC were compared with 116 adolescents without access to an SBHC. Main Outcome Measures: The use of primary and subspecialty medical, mental health, and substance abuse treatment services; the use of after-hours (emergent or urgent) care; and comprehensive preventive health supervision visits and documentation of screening for highrisk health behaviors. Results: Adolescents with access to SBHCs were more than 10 times more likely to make a mental health or substance abuse visit (98% of these visits were made at the SBHC) (PϽ.001). Adolescents with SBHC access had an after-hours (emergent or urgent) care visit rate of 0.33 to 0.52 visits per year less (38%-55% fewer visits) than adolescents without SBHC access, and, overall, made almost 1 additional medical visit per year. A greater percentage, 80.2%, of adolescents with access to SBHCs had at least 1 comprehensive health supervision visit compared with 68.8% of adolescents without access (P=.04). In addition, the adolescents with access were screened for high-risk behaviors at a higher rate. Conclusions: School-based health centers seem to have a synergistic effect for adolescents enrolled in managed care in providing comprehensive health supervision and primary health and mental health care and in reducing after-hours (emergent or urgent) visits. School-based health centers are particularly successful in improving access to and treatment for mental health problems and substance abuse.