Nutritional status affects well-being and survival in patients who are undergoing hemodialysis. It was examined how maintenance hemodialysis altered body fat mass. In 72 patients with chronic renal failure (age, 62 +/- 12 yr; 42 men, 30 women), body fat was measured by dual x-ray absorptiometry 1 mo after initiation of maintenance hemodialysis and approximately 1 yr later (mean +/- SD, 11 +/- 2 mo). The second measurement showed significantly greater body fat mass than the first (11.38 +/- 3.84 versus 10.09 +/- 4.12 kg; P < 0.0001). After calculation of the change in body fat mass per month, no significant differences were evident in relation to gender or to presence of diabetes. Changes in body fat mass per month correlated negatively with baseline serum albumin concentration (r = -0.449, P < 0.0001) and baseline body fat mass (r = -0.423, P < 0.001). These factors independently influenced the change according to multiple regression analysis (R(2) = 0.323, P < 0.0001). In conclusion, body fat mass increases significantly in the first year of maintenance hemodialysis, especially in patients with poor nutritional status. More general, dual x-ray absorptiometry assessment of body fat mass was found to be useful for evaluating the nutritional status of hemodialysis patients.