Twenty-four patients underwent biopsy or resection of the liver for focal nodular hyperplasia (FNH) at Memorial Sloan-Kettering Cancer Center from 1978 to 1988. Twenty-two of the patients were women. The mean age was 35 years. A history of antecedent oral contraceptive or conjugated estrogen (Premarin) use was obtained in 18 of 21 women. There were two men, aged 26 and 37 years; neither gave a history of hormone use. Most of the tumors were solitary (22 of 24) and located in the left lobe of the liver (17 of 22). Fifteen of the patients had a prior or simultaneous malignant lesion and six had other benign tumors. Most of the tumors were resected with a wedge or subsegment of liver (13 of 24). Four patients underwent segmentectomy and five required lobectomy for removal of the tumors. Two patients had an intraoperative biopsy only. The patients in whom the tumor was diagnosed preoperatively underwent computed tomography and arteriography routinely. Scintigraphy of the liver with sulfur colloid was obtained in only three patients, despite its distinct potential for nonoperative diagnosis of FNH.