Data on 378 (in females) and 165 (in males) cases of primary liver tumors reported by 477 hospitals in the United States during 1970 to 1975 show that in males, 91.5% of the tumors were malignant, and in females, 43.9% were malignant and 59.1% were benign. Of the 212 benign tumors in females, 96 were hepatic cell adenomas and 58 were focal nodular hyperplasias. A history of oral contraceptive use was found in nearly half of all women: 65% with benign tumors, 74% with hepatic cell adenomas, and 74% with focal nodular hyperplasias. Symptoms were more severe among users. No case of intraperitoneal bleeding was observed in nonusers. The findings confirm the suggested association between oral contraceptive use and hepatic cell adenomas and focal nodular hyperplasias.