Ingestion of mushrooms containing psilocybin produces hallucinogenic effects and has become a popular form of substance abuse among some adolescents and young adults. We have reviewed the medical literature on psilocybin mushrooms and describe current patterns of use, provide background material on the botony and pharmacology of these crude drugs, and report results of a small study on usage patterns among identified adolescent drug abusers. Among 174 adolescents already identified as substance abusers, 45 (26%) reported having used hallucinogenic mushrooms, frequently in conjunction with alcohol or other drugs. An average intake of 2-4 mushrooms was obtained for about +8, and led to intoxication for 5-6 hours. Mixing of intoxicants such as alcohol, marijuana, and psilocybin mushrooms was the rule. The acute adverse reactions may have been the result of drug synergy. Pediatricians should become aware of the specific patterns of the use of hallucinogenic drugs by adolescents and consider the possibility of such use when evaluating a delirious or psychotic adolescent.