As part of the Medical Case Review Study mandated by the US Health Care Financing Administration, the Trans-Atlantic Renal Council obtained urea kinetic data on 244 patients. When analyzed by body weight, the mean Kt/V urea for the 35 patients weighing more than 1 standard deviation over the mean (over 88.1 kg) was 0.943, compared with 1.106 for the remaining 209 patients (p = 0.007). The high body weight (HBW) patients were 54% more likely to have a Kt/V less than 1.0 than the remaining patients (68.6% of HBW patients versus 44.5% of control patients, p = 0.009). Two-way analysis of variance showed that the tendency to underdialyze HBW patients was present across facilities. Even with the availability of urea kinetic data, HBW patients tend to be less well dialyzed than those of lower body weight.