This study investigated the prevalence of mental health problems among girls who are involved in child welfare or juvenile justice systems. The sample consisted of 1,193 girls ranging in age from 4 to 18, the majority (82.3%, n = 982) of which were older than age 12. Differences based on race/ethnicity and developmental age groups were examined. Consistent with other research, this study found that the mental health needs of girls involved in the child welfare or juvenile justice systems are several times higher than in the general population. Intervention approaches must be developed that take into consideration differences in gender, age, and racial and ethnic group.