: To examine cross-sectional associations between social capital constructs and 1) adolescent lifetime mental disorders, 2) severity of functional impairment, and 3) psychiatric comorbidity.: Data were from the National Comorbidity Survey Adolescent Supplement, a nationally representative mental health survey of 6,483 U.S. adolescents aged 13-18 years. Information from fully-structured diagnostic interviews, including adolescent and caregiver reports, was used to measure seven social capital constructs and lifetime DSM-IV mental disorders (mood, anxiety, behavior, substance use and eating disorder classes). Disorder severity was divided into severe vs. mild/moderate. Comorbidity was measured as the number of different classes of lifetime mental disorders.: Adjusted for socio-demographics and caregivers' mental health, the most consistent associations with adolescent mental disorder were for supportive friendships (any disorder OR = 0.95, 95%CI = 0.91-0.99), family cohesion (OR = 0.81, 95%CI = 0.75-0.86), school bonding (OR = 0.76, 95%CI = 0.71-0.81), and extracurricular participation (OR = 0.90, 95%CI = 0.86-0.95), although results differed by disorder class. Caregiver-reported neighborhood trust and reciprocity and caregiver community involvement were less consistently associated with mental disorder. Medium levels of adolescent-reported affiliation with neighbors was associated with lower odds of mood (OR = 0.81, 95%CI = 0.66-0.98) and anxiety (OR = 0.78, 95%CI = 0.64-0.96) disorder, while high levels were associated with higher odds of behavior disorder (OR = 1.47, 95%CI = 1.16-1.87). Several associations were stronger for severe vs. mild/moderate disorder and with increasing comorbidity.: Although we cannot infer causality, our findings support the notion that improving actual and/or perceived social capital, especially regarding friendships, family, and school, (e.g., through multimodal interventions) could aid in the prevention and treatment of both individual adolescent mental disorders and psychiatric comorbidity.