A 26-year-old pregnant woman was diagnosed as having hepatocellular carcinoma at 16 weeks of gestation when extremely high levels of alpha-fetoprotein were found on a routine screening examination. The pregnancy was terminated, and a right hepatectomy was performed. Although such cases are rare, this one suggests that early measurement of maternal serum alpha-fetoprotein in a pregnant woman with hepatitis B surface antigenemia may allow the timely detection of a hepatocellular carcinoma.