The prevalence of obesity is increasing among long-term hemodialysis patients. BMI is not a reliable indicator of adiposity because it does not differentiate between subcutaneous fat, visceral fat, or muscle. This problem can be exacerbated in disease states such as ESRD treated by hemodialysis, in which muscle may account for a smaller percentage of body weight because of wasting or edema. The poor diagnostic performance of BMI may potentially explain the paradoxical association between higher BMI and lower mortality.