The Longitudinal Epidemiologic Study to Gain Insight into HIV/AIDS in Children and Youth (LEGACY) study is a prospective, multisite, longitudinal cohort of U.S. HIV-infected youth. This analysis was limited to perinatally HIV-infected youth (n=197), 13 years and older, with selected variables completely abstracted from HIV diagnosis through 2006. We evaluated relationships between ever having one or more nonsubstance related medically documented psychiatric diagnoses and three risky health behaviors (substance abuse, preadult sexual activity, and treatment adherence problems) recorded between 2001 and 2006. Logistic regression was used for all binary outcomes and participant age was included as a covariate when possible. All 197 participants included in the analysis were prescribed antiretroviral therapy during the study period; 110 (56%) were female, 100 (51%) were black non-Hispanic, and 86 (44%) were Hispanic; mean age at the last visit was 16.8 years, ranging from 13 to 24 years. One hundred forty-six (74%) participants had a history of at least one risky health behavior. There were 108 (55%) participants with at least one medically documented psychiatric diagnosis, 17 (9%) with at least one record of substance abuse, 12 (6%) with documented preadult sexual activity, and 142 (72%) participants with reported adherence problems. In the final model, a history of at least one psychiatric diagnosis was associated with having at least one of the three risky behaviors (odds ratio [OR]=2.33, p=0.015). There is a need for a continued close partnership between HIV specialty care providers and mental health services treating perinatally HIV-infected youth with an added focus on improving treatment adherence.