Based on strict predefined histologic criteria, we identified 23 patients with hepatic adenoma and 41 patients with focal nodular hyperplasia seen at this institution between 1961 and 1980. Patients with hepatic adenoma were young and 91% were female. When a reliable history was available, 89% had used oral contraceptives; 53% presented acutely or with pain. Eleven of 11 radionuclide scans were abnormal; 15 of 15 angiograms showed a hypervascular mass with 7 of 15 showing areas of hypovascularity. Eighteen resections were performed with one operative death. Two tumors contained areas of unequivocal hepatocellular carcinoma. Fifteen of 18 patients followed for 82 +/- 11 mo were living and well and had discontinued oral contraceptives. Focal nodular hyperplasia patients were older, 88% were female, and 58% had used oral contraceptives. Their lesions were discovered accidentally. Seven of 12 radionuclide scans demonstrated voids, while 13 of 13 angiograms showed hypervascular lesions with no areas of hypovascularity. Seventeen tumors were resected. Twenty-three of 24 patients followed for 45 +/- 7 mo were living and well. One died of nonhepatic causes. Based on the findings of this review, we believe that if the clinical suspicion of hepatic adenoma or focal nodular hyperplasia is strong, elective laparotomy for diagnosis is usually the best approach. Hepatic adenoma should be resected if technically feasible. Intraoperative wedge biopsy is appropriate for focal nodular hyperplasia.