The pathologic features, clinical presentation and natural history of hepatocellular carcinoma (HCC) developing in the noncirrhotic liver were studied in 61 patients against a background of 63 patients seen concurrently with HCC complicating cirrhosis. Noncirrhotic HCC had a bimodal age distribution, with females predominating the first age-clustering (10-50 years) and males predominating the second age-clustering (50-90 years). Cirrhotic HCC had a unimodal age distribution (40-90 years) with male dominance throughout. Estrogen exposure was noted in 57% of the noncirrhotic HCC women overall and in 80% of those in the younger age-clustering. The majority of noncirrhotic HCC presented with a single hepatic mass or a dominant primary with satellite lesions in contrast to the usual multinodular or diffuse disease seen with cirrhosis. Twenty-nine noncirrhotic patients survived complete resection of disease limited to the liver and exhibited a median survival of 2.7 years with a 5-year survival of 25%. Low histologic grade, minimal necrosis, and the absence of hemoperitoneum, hepatomegaly, and adjacent organ involvement were all favorable prognostic variable. Patients with metastatic or locally unresectable noncirrhotic HCC had a median survival of 9 months, and 24% survived in excess of 2 years. This survival experience is significantly more favorable than cirrhotic HCC patients, who had only a 1.2-month median and a 3% 2-year survival. Low histologic grade, mild mitotic activity and the presence of some fibrosis within the specimen were associated with a favorable outcome in advanced noncirrhotic HCC. The favorable prognosis and heterogeneous composition of the noncirrhotic, when compared to the cirrhotic HCC cohort, may be important considerations in the design and evaluation of future clinical trials.