A comparison of personality factors on scales of the Minnesota Multiphasic Personality Inventory-Adolescent (MMPI-A) was conducted with a sample of adolescents referred to a residential substance abuse treatment program. A total of sixty adolescents identified with hallucinogen (n = 20), cannabis (n = 20), or methamphetamine (n = 20) as their drug of choice participated in the study. All adolescents met criteria for hallucinogen, cannabis, or methamphetamine dependence in accordance with their assigned groups. Adolescents were matched by age and gender. Primary analysis revealed significant differences between hallucinogen and cannabis groups on the Hypochondriasis (Hs), Schizophrenia (Sc), and Adolescent-Bizarre Mentation (A-biz) scales. Post hoc analyses on remaining Clinical, Content, and Validity scales revealed significant differences between hallucinogen and cannabis groups on the Infrequency (F) scale. Scores on all scales of the methamphetamine group were not significantly different from scale scores on the cannabis or hallucinogen groups. Although sample sizes were small, this is one of the first studies to utilize personality assessment in order to differentiate personality characteristics of adolescents who report hallucinogen (i.e., psilocybin mushroom), cannabis, or methamphetamine as drug of choice.