The liver is an estrogen responsive organ. Clinically, estrogens may play a role in the induction of liver tumors and, experimentally, estrogens are involved in the control of hepatocyte proliferation. The results of a prospective controlled clinical trial using an anti-estrogen, tamoxifen, in patients with unresectable hepatocellular carcinoma (HCC) are presented below. Thirty-eight consecutive cirrhotics with HCC were allocated to either 30 mg/day tamoxifen or no treatment. The two groups of patients were matched for mean age, male/female ratio, Child-Pugh risk group, approximate tumor volume (US and/or CT scan) and etiology of the underlying cirrhosis. The drug appeared to have no side effects. Survival was significantly prolonged in tamoxifen-treated patients with 22% (vs. 5%) survival at 12 months. No differences were observed between males and females or alcoholic and non-alcoholic cirrhosis. In 53% of tamoxifen-treated patients the levels of alpha-fetoprotein dropped and, in this subgroup, survival was further prolonged. Tumor volume, lactate dehydrogenase (LDH) and alkaline phosphatase slowly increased, suggesting a slower, but continuous, progression of the disease. In conclusion, anti-estrogen treatment appears effective in the palliation of unresectable or otherwise untreatable HCC. A reduction in alpha-fetoprotein levels appears to be a favorable prognostic index.