Bulimia nervosa, a common eating disorder usually characterized by binge eating and self-induced vomiting, may also involve abuse of prescription diuretics. This article describes four patients who abused prescription diuretics in large quantities (up to 2 g/d of furosemide) for extended periods of time. Physical examination and laboratory values provided few clues to the diagnosis of bulimia nervosa. Other eating-related behaviors previously linked to bulimia nervosa--including abuse of diet pills, illicit amphetamines, and laxatives, as well as withholding of insulin in one diabetic patient--were present in these cases. Usually the patients' primary physicians were not aware of these problems. Physicians should be aware that patients requesting prescription diuretics may have bulimia nervosa.