Over a 14-year period, 435 patients underwent renal transplantation. Chronic rejection has occurred in 58 (13%) of all grafts and has accounted for 18% of all graft losses. After the first 6 months following transplantation, chronic rejection was the most common cause of graft failure, accounting for 40% of losses. The median time (interquartile range) from transplantation to graft failure was 3 years (2-5.5 years). Comparison of azathioprine versus cyclosporin treated patients showed no significant difference in the incidence of graft loss (Cox regression score 2.55, P = 0.11). Furthermore, there were significantly more grafts with deteriorating function owing to chronic rejection in cyclosporin-treated patients (n = 16, 11% of surviving grafts) than in azathioprine-treated patients (n = 2, 3% of surviving grafts). These data suggest that cyclosporin does not prevent the development of chronic rejection in renal transplants.