The available data underestimate the use of drugs, because they exclude school dropouts, youth who are incarcerated or in treatment settings, and other youths. These omitted subgroups may contain the troubled youth most in need of assistance. Nevertheless, the data show cultural and ethnic differences, gender differences, the influences of families and peers, the role of emotional and behavioral difficulties, and the role of school failure in drug use. Findings suggest the need for prevention programs that focuses systematically on young children at risk for learning and behavior problems, for parent training, and for treatment that provides alternative and culturally appropriate coping skills. 80 references.