Recent studies have indicated significant levels of co-morbidity between substance use disorders (SUD’s) and other psychiatric disorders in samples of adolescents undergoing treatment for substance abuse. In particular, there are high prevalence rates for negative affect disorders such as major depression (MDD) and post-traumatic stress disorder (PTSD) in community and treatment samples of adolescents reporting substance abuse or substance dependence. While most adolescents presenting with MDD do not report co-occurring problems with substance misuse, patterns of substance misuse are significantly associated with elevated levels of depressive symptoms. This study was an attempt to examine heterogeneous relations among depressive symptoms and drinking motives in a sample of adolescents in substance abuse treatment. Data were collected from 120 adolescents and young adults (87 male, 33 female, mean age 17.2 years) undergoing substance abuse treatment at facilities in South Florida. Using cluster analysis, participants were grouped into four distinct and meaningful subgroups based on patterns of depressive symptoms and motives for drinking before sex. Analysis of the data identified a subgroup of adolescents with high levels of depressive symptoms and drinking motives who are at elevated risk for HIV/STD exposure due to higher levels of risky sexual behavior and altered sexual behavior related to co-occurring alcohol use. The results of the study have several implications for clinical practice. First, the high prevalence of risky sexual behaviors in this sample shows the pressing need for HIV/STD prevention programming for this population. Second, substance-abusing youth in treatment are a heterogeneous group, with subgroups discernible from one another on multiple characteristics. Third, the subgroup found to be a highest risk for HIV/STD exposure included an overrepresentation of females (46.2 percent) in contrast to the remaining three groups (12.9 percent to 40.9 percent). Finally, the findings indicate that adolescents in substance abuse treatment have clinically significant problems beyond just substance abuse. Study limitations are discussed. 4 tables and 52 references