We describe three men and two women, aged 18-50, with an occasional finding of increased aspartate and alanine aminotransferase and gamma-glutamyl transpeptidase levels in the absence of any drug treatment and past or current alcohol abuse. Two patients were overweight (body mass index 29 and 32, respectively) and physical examination was normal in all but one case. Tests for hepatitis A, B and C, Epstein-Barr virus, cytomegalovirus, toxoplasma and autoimmune hepatitis were negative and metabolic diseases (Wilson's disease, haemochromatosis, alpha-l-antitrypsin deficiency) were excluded by specific tests. Ultrasound liver scan revealed massive steatosis in all patients. Liver histology showed diffuse steatosis and parenchymal inflammation in all cases, with concomitant fibrosis and Mallory bodies in three of them. Findings were consistent with non-alcoholic steatohepatitis, a rare condition with potential progression to cirrhosis in a minority of cases. This disease, for which no treatment is currently available, must be considered in all subjects with elevated aminotransferases, in the absence of known causes of liver damage.