Liver biopsies with a main histological diagnosis of steatosis were selected from 3,422 liver biopsies carried out in our department between January 1995 and December 1998. Patients with known risk factors for steatosis, such as excessive alcohol consumption, hepatitis C infection, treatment with amiodarone, perhexiline maleate, tamoxifen, antiviral drugs (didanosine, zidovudine) methotrexate, sodium valproate or total parenteral nutrition, Wilson's disease and organ transplant were subsequently excluded. Of the 43 liver biopsies finally included in the study, 23 showed simple steatosis and 20 steatohepatitis. Eighty-one per cent of the patients were male (mean age of 44 years) and the majority were asymptomatic. The most frequent indication for liver biopsy was hypertransaminasemia. No differences were observed between the two groups in terms of frequency and severity of classical risk factors for steatosis (diabetes mellitus, dyslipemia and obesity). Thirty-five percent of patients with steatohepatitis and 26% of those with simple steatosis had none of these risk factors. Patients with steatohepatitis were older than those with simple steatosis. They presented more severe symptomatology, the degree of steatosis was more intense and laboratory investigations showed greater alterations. These results suggest that simple steatosis and nonalcoholic steatohepatitis are two different phases of the same disease. The difficulty in clinical differentiation justifies carrying out liver biopsy, especially in patients with more severe symptomatology whose laboratory results show greater alterations, since these patients present more marked histological lesions, are at risk of developing liver cirrhosis and require therapy.