An increase in obesity prevalence among patients who initiate dialysis may influence the growth of the total ESRD population as a result of improved survival and decreased likelihood for transplantation. Temporal trends in mean body mass index (BMI) and obesity prevalence were examined among incident patients with ESRD by year of dialysis initiation between 1995 and 2002, and these trends were compared with those in the US population during this same period. Among incident dialysis patients, BMI was calculated with the height and estimated dry weight collected from the Centers for Medicare and Medicaid Services End-Stage Renal Disease Medical Evidence Form. In the US population, self-reported height and weight were used. Prevalence of total obesity and obesity stage > or =2 were defined as a BMI > or =30 and > or =35 kg/m(2), respectively. Among incident patients with ESRD, mean BMI increased from 25.7 to 27.5 kg/m(2), and total obesity and obesity stage > or =2 increased by 33 and 63%, respectively, among incident patients with ESRD (P < 0.0001 for obesity trends). BMI slope was approximately two-fold higher in the incident ESRD population compared with the US population for all age groups. However, temporal increases in obesity prevalence were similar between the two populations. As a result of the survival advantage associated with obesity and decreased likelihood for transplantation, these trends most likely will influence the total number of patients who receive dialysis in the next decade.