During a study of drug incidents dealt with in one month by 62 casualty departments in Greater London, 395 drug-dependent individuals were identified. The great majority of these patients were seen in hospital following an overdose, and barbiturates were the drugs used most frequently. A high incidence of multi-drug use was noted, and many individuals had obtained their drugs from an illicit source. A history of repeated overdosing was common, and one fifth of the patients behaved aggressively while they were in casualty. The implications of these findings are discussed, with particular reference to the demands that are made on casualty departments by drug-dependent individuals.