Fenfluramine is a substituted phenylethylamine structurally related to amphetamine. Within three hours following the ingestion of 1,600 mg of fenfluramine, a 17-year-old girl, who was initially agitated and had tachycardia, developed convulsions, cardiac arrhythmia, and cardiorespiratory arrest. In previously reported cases, flushing, sweating, mydriasis, tachycardia, and agitation commonly occur, as well as convulsions and abrupt cardiorespiratory arrest. The rapid onset and progression of symptoms, the short interval between ingestion and death, and the lack of responsiveness to resuscitative measures are common findings in fatal cases.