Immunological rejection is the most important cause of kidney transplant failure. Recently, nonimmunological causes of long-term allograft failure have become more widely appreciated. In primary chronic renal disease, blood pressure is of overriding importance for long-term renal function. The role of blood pressure in determining long-term transplant outcome has not yet been established. We studied the influence of blood pressure post-transplantation on long-term kidney graft outcome in 29,751 patients. Outpatient blood pressure measurements were recorded and reported to the Collaborative Transplant Study. Graft and patient survival rates were analyzed over seven years in relation to blood pressure. Increased levels of systolic and diastolic blood pressure post-transplantation were associated with a graded increase of subsequent graft failure (P < 0.0001). Chronic graft failure was significantly associated with blood pressure even when patient death was censored (P < 0.0001). Cox regression analysis established increased blood pressure as an independent risk factor for graft failure. We conclude that post-transplant blood pressure is a highly significant predictor of long-term kidney graft outcome. Whether aggressive lowering of blood pressure improves long-term transplant outcome will have to be studied prospectively.