The clinical significance of liver disease is frequently underestimated in patients with metabolic disorders. In patients followed up in a metabolic unit for diabetes, obesity or hyperlipidemia (n=147), we studied the prevalence and the severity of liver disease, and its relationship with the metabolic syndrome (MS). Cases cared for in a liver unit (n=179) were used as controls. Patients in the metabolic series were older and had a higher prevalence of coronary heart disease. Criteria for the metabolic syndrome were fulfilled in 64% and 22% of cases, respectively (P<0.0001). Liver biopsy was obtained in 44 and 66% of cases. Metabolic patients had a more severe steatosis score (P<0.0001), whereas the scores of fibrosis and necroinflammation were less severe (P=0.0059 and 0.0007, respectively). Histological criteria for non-alcoholic steatohepatitis (NASH) were present in 82% of metabolic cases and 68% cases in the liver series (P=0.057). Liver disease in patients routinely cared for in metabolic units is similar to that observed in patients cared for in liver units, and potentially may progress to terminal liver failure. Liver biopsy is recommended for diagnostic and prognostic purposes, as well as for testing treatment effects in controlled trials.