Adolescents emancipated from the child welfare system at 18 years of age must negotiate the transition to independent adulthood suddenly and without guarantees of continuing support. The nature and severity of mental health problems among older foster youth has important implications because negative outcomes in adulthood are more likely for adolescents with psychiatric disorders. Adolescents in state custody are at risk for psychiatric disorders due to histories of abuse, neglect, abandonment, or parental incapacity and exposure to multiple other familial and environmental conditions associated with the development of psychopathology, This study involves secondary analysis of a large dataset derived by sampling all youth from three Midwestern state child welfare agencies who were 17 years or older and had been in foster care for at least one year. Mental health was assessed with a structured diagnostic interview (CIDI), and information was obtained on their experience of maltreatment, history in the child welfare system, utilization of services, relationship networks and social support, and psychosocial and adaptive functioning. Several analyses are proposed. First, the nature, prevalence, and comorbidity of mental health disorders will be examined, along with variations according to individual and system-level factors (e.g., type of foster placements). Second, latent class analysis will identify particular patterns of abuse and neglect experienced, and these maltreatment profiles will be investigated for specific correspondences with particular mental health disorders. Third, the possibility that links between maltreatment and mental health are moderated by social support and successful foster care intervention will be investigated. Finally, classification and regression tree analysis (CART) will be used on individual, maltreatment, and child welfare factors to develop a predictive model to identify youth likely to exhibit mental health problems. Knowledge of factors and processes associated with mental health problems among foster youth is necessary for providing targeted preventive interventions and treatment services to help them cope with the transition to independence. Furthermore, studying this population presents unique opportunities to examine how trauma and psychosocial factors are linked to mental health in late adolescence.