In a series of 53 fenfluramine intoxications (15 taken from the literature), 10 were lethal after doses of 28.7--70 mg/kg of body weight. Cardiac arrest occurred 1--4 hr after ingestion in 9 cases; all these 9 patients died. Two out of 3 patients with more than 15 mg/kg had coma and convulsions. Other frequent signs were mydriasis, tachycardia, and rubor of the face. The additional signs of nystagmus, hypertonia, trismus, hyperreflexia, clonus, excitation, hyperthermia, and sweating define the clinical syndrome of fenfluramine intoxication. Symptoms begin 30--60 min after ingestion and can persist during several days. Early gastric lavage, instillation of activated charcoal, diazepam in case of seizures, chlorpromazine for malignant hyperthermia, propranolol for extreme tachycardia, and lidocaine in the event of ventricular extrasystoles are recommended. If trismus is a prominent sign, muscle relaxants must be given before gastric lavage can be done. The relatively benign course after survival of the first 4 hr suggests supportive therapy only in the later phase of intoxication.