Excessive weight gain is common after liver transplantation and frequently leads to obesity. This has been attributed to immunosuppression. The aim of the present study was to assess the extent of weight gain and the risk factors for weight gain after liver transplantation. Height and estimated dry weight were collected prospectively in consecutive adult liver-transplant patients, transplanted between January 1996 and October 2001. A total of 597 patients (45% female, median age of 50 years; range 16-73) was studied. Eighty-six percentage was transplanted for chronic liver disease. The median weight gain at 1 and 3 years was 5.1 and 9.5 kg above dry weight pretransplant. By 1 and 3 years, 24% and 31% had become obese (defined as a body mass index (BMI) >30 kg/m(2)). There was no significant difference in weight gain between the sexes, those who were obese before transplantation or those who received corticosteroids for >3 months. Weight gain was significantly greater (P < 0.05) in patients aged >50 years and those transplanted for chronic liver disease compared with fulminant liver failure. A pretransplant BMI >30 was a strong indicator that the patient would still have a BMI >30 at 3 years. There was no effect of the type of immunosuppression on weight gain. Obesity is common in the liver transplant population, but it seems to be unrelated to any specific immunosuppressive drug. The greatest weight gain occurs after the first 6 months and intervention with dietary advice at this point could be implemented to minimize the long-term morbidity and mortality risks associated with obesity.