To discuss the forms of cocaine that are available and their methods of administration and to review the medical complications of cocaine abuse. Pertinent articles were identified through a MEDLINE search of the English-language literature from 1986 to 1992 and through a manual search of bibliographies of all identified articles. All articles describing complications of cocaine use were either case reports, review articles, or small series. No controlled studies on the subject were available. A qualitative description of reported complications without the use of quantitative methods. Multiple complications of cocaine use have been described and are often related to the method of administration of cocaine. Since the introduction of freebase and "crack" cocaine, new complications have been noted, and nearly all organ systems have been affected. Indirect complications, related to violent behavior and infectious diseases, are also important consequences of cocaine use. Adverse reactions to cocaine use should be considered in the differential diagnosis of various disorders, particularly ischemic events in young adults. The actual frequency of each complication is unknown.