Fenfluramine has been used for a number of years as a short-term adjunct to diet in the management of obesity. Controlled studies and clinical experience have shown that it possesses anorectic activity at least as good as that of other therapeutically useful drugs of its type, but like these drugs it has only a limited role in the overall management of obesity. Tolerance to the anorectic effects of fenfluramine may possibly develop more slowly than to other chemically related drugs in patients with refractory obesity. The mechanism of its anorectic action is probably by an effect on the appetite control centres in the hypothalamus, rather than by an effect on glucose and lipid metabolism. However, its effect in enhancing glucose uptake into skeletal muscle may be of advantage in diabetes mellitus, preliminary studies suggesting that it is of potential use in maturity-onset obese diabetics who cannot be adequately controlled by dietary measures alone. The starting dosage in obesity of 40mg daily should be increased gradually over 2 to 4 weeks to 60 to 120mg. In general, little extra benefit is gained by higher dosage. When a course of therapy is to be discontinued, fenfluramine dosage should be reduced gradually over a period of 2 to 4 weeks in order to avoid mood depression which has occurred in some patients on abrupt withdrawal of the drug. With these recommendations, the majority of patients tolerate fenfluramine satisfactorily, although some patients may have to discontinue the drug because of troublesome gastro-intestinal problems, diarrhoea, drowsiness or dizziness. Unlike other amphetamine-derived anorectics, fenfluramine is not a central stimulant in therapeutic doses, and it probably has little abuse potential.