Improvements in long-term kidney graft survival have been recently noted. However, the reasons for this were unclear. This study examined post-transplant renal function within the first year as an independent variable influencing long-term survival. The influence of demographic characteristics (age, sex, race); transplant variables (cadaver versus living donor, cold ischemia time, HLA mismatching, delayed graft function and transplant year), and post-transplant variables (immunosuppressive agents for the prevention of acute rejection, clinical acute rejection and post-transplant renal function in the first year) on graft survival were analyzed for 105,742 adult renal transplants between 1988 and 1998. Renal function in the first year was expressed as serum creatinine at six months and one year and delta creatinine (change in serum creatinine between 6 months and 1 year). Graft half-life was used to measure long-term survival. During this 11-year period, the one-year serum creatinine values for cadaver recipients steadily improved, from 1.82 +/- 0.82 mg/dL in 1988 to 1.67 +/- 0.82 mg/dL in 1998 (P and < or =50 years. The Relative Hazard (RH) for graft failure was 1.63 (1.61, 1.65; P < 0.0001) with each increment of 1.0 mg/dL of serum creatinine at one year post-transplant and it increased to 2.26 (2.2, 2.31; P < 0.0001) when the Delta creatinine was 0.5 mg/dL. The RH reduction for graft failure was substantially lower for the years 1993, 1996, 1997 and 1998 when post-transplant renal function was not included in the model (P < 0.05). However, the RH reduction per year was not different when post-transplant creatinine was included in the model, 1.01 (0.94 to 1.05; P = 0.89). In conclusion, one-year creatinine and Delta creatinine values predict long-term renal graft survival. Recent improvements in graft half-life are related to conservation of renal function within the first year post-transplantation.