In patients with nonalcoholic fatty liver disease (NAFLD) isolated steatosis is considered a benign condition with no or minimal rate of progression, in contrast to nonalcoholic steatohepatitis (NASH) which can progress to cirrhosis. We report on a series of six patients with isolated steatosis on an initial liver biopsy, and NASH on a follow-up biopsy performed five years after. All but one of the initial biopsies were longer than 15 mm. At follow-up, inflammation and ballooning were present in all patients and mild fibrosis in three. All patients had one or more features of metabolic syndrome at baseline. Progression to steatohepatitis occurred independent of aminotransferase changes. Five patients experienced an increase in one or several metabolic risk factors during follow-up: body mass index, triglyceride levels, arterial hypertension and/or the HOMA index. One patient did not exhibit progression but was still exposed to metabolic risks factors at the end of follow-up. This report demonstrates that isolated steatosis is not necessarily a benign, non-progressive condition. Current recommendations for the absence of hepatic monitoring in patients with isolated steatosis are not adequate. If metabolic risk factors persist or deteriorate during follow-up and/or non-invasive markers suggest disease progression, a control liver biopsy should be considered.