Background. There are no large studies of the effect of pretransplant dialysis status on the outcome of renal transplantation (Tx) in children. This study evaluated the North American Pediatric Renal Transplant Cooperative Study (NAPRTCS) registry data for the outcome of Tx in pediatric patients who either (1) received their transplants preemptively or (2) were maintained on dialysis before receiving their transplants. Methods. We compared graft survival and patient survival rates, incidence of acute tubular necrosis (ATN), acute rejection episodes, and causes of graft failure in peritoneal dialysis (PD) patients with those maintained on hemodialysis (HD) and those undergoing preemptive Tx (PTx). Results. Primary Tx was performed in 2495 children (59% male; 61% Caucasian; 1090 PD, 780 HD, 625 PTx) between 1/1/1992 and 12/31/1996. The overall graft survival rates of the PD and HD groups were similar, but were less than that of the PTx group (3- year: 82% PD and HD, 89% PTx, overall P=0.0003). Improved graft survival in the PTx group was present only in recipients of grafts from living donors. There was no difference in the overall patient survival rate at 3 years, or in time to first acute-rejection episodes in the three groups. The incidence of ATN in the first 7 days post-Tx was higher in PD and HD patients than in PTx patients (11% PD and 12% HD vs. 2% PTx, P<0.001; HD vs. PD, P=NS). The major single cause of graft failure in each group was: PD, vascular thrombosis (20%); HD, chronic rejection (27%); PTx, acute and chronic rejection (21% each). Conclusion. NAPRTCS data show that graft survival is improved in patients receiving PTx, compared with those receiving PD and HD. Graft loss resulting from vascular thrombosis is more common in children who receive PD than in those receiving HD.