For this study, we analyzed the role of rejection in graft failure in children. Rejection results were examined after 3004 pediatric renal transplants (1367 living donor, 1637 cadaver source). A total of 3453 (1298 living donor, 2155 cadaver source) rejection episodes have occurred, for rejection ratios of .95 for living donor and 1.32 for cadaver source transplants, with a constant difference of 18% points after four months, in the percentage of patients ever experiencing a rejection. Rejection results were examined by patient age (0-1 vs. 2-5 vs. 6-12 vs. > or = 13). Rejection ratios, annualized rejection frequency, time to first rejection, and mean number of rejections for patients with rejection were not elevated in the younger patients. However, for the initial rejection episode, recipients less than six years of age had significantly (P < .001) poorer outcome from the rejection episode with an increased risk of graft failure in both donor source groups. This age effect on rejection outcome is only seen with the first rejection episode and is not observed with subsequent rejection episodes.