Recent epidemiologic studies using existing population-based health datasets repeatedly find elevated risk for mental health morbidity and mental health services use among lesbians, gay men or individuals likely to be of minority sexual orientation. In particular, greater than expected prevalences of stress sensitive disorders (e.g. depression, anxiety, and substance use dependency) have been repeatedly observed. Unfortunately, current methodological limitations in the existing datasets (primarily low statistical power, indirect measurement of sexual orientation, and lack of measurement of probable sexual orientation-specific effect modifiers) hampers understanding of the mental health services needs in this at risk population. In response to NIMH PA-01-096, the current application proposes to capitalize on information available from the biennial California Health Interview Survey (CHIS) to examine mental health morbidity and mental health-related services use among lesbians and gay men. We will reinterview a systematic sample of 2,700 CHIS II participants, oversampled for minority sexual orientation, to conduct an assessment of the relationships among mental health, substance use, and sexual orientation-specific issues. We will compare individuals varying in sexual orientation in order to investigate differences in prevalence of mental health and substance use morbidity, patterns of mental health and substance use comorbidity, and use of mental health and substance-related services. A second goal is to identify factors that modify mental health/substance use morbidity risk among lesbians and gay men, including HIV infection status, experiences with discrimination, levels of social support, and neighborhood characteristics. A further goal is to investigate, among those seeking services, sexual orientation-specific differences in barriers and obstacles to receiving care, indicators of services quality, and levels of satisfaction. Findings will clarify the nature and basis of excess risk for mental health/substance use morbidity among those of minority sexual orientation, as well as identify factors that promote resiliency. Results will also provide critical information about problems in service delivery, assisting efforts to design effective interventions.