A 34-year-old man had asymptomatic hepatomegaly, slightly increased serum alanine aminotransferase and gamma-glutamyl transpeptidase levels, and a sonographic pattern suggesting diffuse hepatic steatosis. Liver biopsy revealed fatty change in 25% to 50% of hepatocytes. The patient also had low serum levels of cholesterol and triglycerides and met clinical, biochemical, and familial diagnostic criteria of heterozygous hypobetalipoproteinemia. We could not relate his hepatic steatosis to any already known cause of fatty liver and could only attribute it to heterozygous hypobetalipoproteinemia. Familial heterozygous hypobetalipoproteinemia should be ruled out in patients with unexplained hepatic steatosis.