A rare benign neoplasm of the liver. Mean age at diagnosis is 34 years and the disease rarely occurs in children. Most patients are asymptomatic and lesions are found incidentally during laparotomy or radiologic studies performed for other reasons. In most cases, adenomas develop for unclear reasons in an otherwise healthy liver. Some predisposing conditions have been identified: prolonged oral contraceptive use, glycogenosis type III and IV, congenital portocaval shunt and, in males, use of anabolic steroids. Malignant transformation is rare and the long-term prognosis is good.