The relation between psychological characteristics and drug use was investigated in subjects studied longitudinally, from preschool through age 18. Adolescents who had engaged in some drug experimentation (primarily with marijuana) were the best-adjusted in the sample. Adolescents who used drugs frequently were maladjusted, showing a distinct personality syndrome marked by interpersonal alienation, poor impulse control, and manifest emotional distress. Adolescents who, by age 18, had never experimented with any drug were relatively anxious, emotionally constricted, and lacking in social skills. Psychological differences between frequent drug users, experimenters, and abstainers could be traced to the earliest years of childhood and related to the quality of parenting received. The findings indicate that (a) problem drug use is a symptom, not a cause, of personal and social maladjustment, and (b) the meaning of drug use can be understood only in the context of an individual's personality structure and developmental history. It is suggested that current efforts at drug prevention are misguided to the extent that they focus on symptoms, rather than on the psychological syndrome underlying drug abuse.