A prospective study was undertaken in order to investigate the association between clinical and biochemical parameters and the histopathological findings in liver biopsies in the morbidly obese. Wedge liver biopsy specimens were taken at the beginning of the surgical procedure from 100 consecutive morbidly obese patients undergoing Roux-en-Y gastric bypass. Histological abnormalities were found in almost all of the examined material (98 of 100), which ranged from mild fatty infiltration through inflammatory change and alcoholic hepatitis-like change to fibrosis and cirrhosis. The patients with abnormalities were divided into two groups: those with a single abnormality (n = 56) and those with two or more histopathological findings (n = 42). Age, excess body weight, total cholesterol and triglyceride levels were significantly higher in the group with more than one histopathological finding. In a discriminant function analysis, it was found that the preoperatively available measures of age, sex and excess body weight, as well as ALT and triglyceride levels, could discriminate between the two patient groups. A model which uses these variables has been described which correctly assigns the patients to their histology groups in 73% of the cases. This model could provide a useful noninvasive clinical tool for the preoperative evaluation of possible hepatic damage in morbidly obese patients in whom there is no other known cause of possible liver disease.