From 1970 to 1991 244 kidney transplantation were performed in 203 children at Medical School Hannover. In 32% acute renal failure (ARF) happened. The most frequent cause of ARF was acute graft rejection in 21%, followed by tubular necrosis in 19%. Other causes were 18% urologic and 15% vascular complications, 9% infections, 8% hemolytic-uremic syndrome, 5% nephrotoxicity and acute bleeding each. The outcome was different according to the varying causes. In 51% the ARF led to graft loss. Progress in immunosuppressive treatment as well as in diagnostic instruments like Doppler sonography will reduce the high amount of graft loss after ARF.