In 1992 the half-life of living-related donor transplant recipients in the UCLA registry was 9-12 years, and for cadaver donor recipients it was 7.7-8.6 years. We present half-life data in pediatric renal transplants in the North American Pediatric Renal Transplant Co-operative Study (NAPRTCS) registry. An analysis of post 1 year graft survival was performed for the 1424 living donor and 1338 cadaver donor transplants that were successfully functioning at 1 year in the NAPRTCS. Exponential survival curve and proportional hazards survival analyses were performed. The 1987 living donor cohort had a post 1 year graft survival of 11.2 years, while cohorts for 1991 and beyond exceeded 18 years. For cadavers, half-life for annual cohorts has changed from 8.8 years in 1987/88 to 13.7 years in 1991 and beyond. Variance estimates increase in later years because of the decreased number of events and follow-up years. Because follow-up for functioning grafts is reported only semi-annually, while graft failures can be reported at any time, the estimates are negatively biased with the effect increasing with the later cohorts. For the 1987 cohort the effect is negligible, but for 1993 entrants the effect could cause an understatement of half life by up to 40%, although its exact magnitude is unknown. Proportional hazard analyses indicate a significant linear cohort effect for both donor groups with improvement in post 1 year graft survival for later years. Donor source, prior transplant, prior dialysis, recipient race and cyclosporine dose are each simultaneous prognostic factors for continued graft survival. Recipients of antibodies at transplant, differing transfusion histories, HLA matching groups and very young recipients were not found to be at differential risk. CONCLUSION: This review documents a substantial increase in post 1 year graft survival for living donor transplants and a smaller statistically significant trend for cadaver transplants. A continued advantage for living donor versus cadaver donor transplants after the first transplant year is also observed.