Experience with renal allograft fracture occurring in 21 of 246 transplants performed over a 29-month period is reviewed. Clinical manifestations included pain and tenderness at the graft site, fever, and falling hematocrit. The fracture occurred without exception in the course of an acute rejection episode. Diagnosis was made from two days to seven weeks following transplantation; in 13 patients (62%) diagnosis was made within two weeks of surgery. Severe damage to the kidney necessitated nephrectomy in all but two transplants. Of those not removed at initial exploration only one regained function to permit a dialysis-free existance for several months. Histologic examination of the fractured kidneys revealed the pathogenesis to be acute rejection in 13 (62%), accelerated acute rejection in four (19%), and a combination of these processes in four (19%). Conclusions from this study are that fractures of renal allografts: (1) are more frequent than commonly realized; (2) are primarily due to the swelling of acute rejection; (3) are often characterized by sudden onset of pain in the region of the graft accompanied by fever and falling hematocrit; (4) should be treated by prompt surgical intervention to control hemorrhage, to perform nephrectomy if indicated, and to evacuate the hematoma in order to reduce the possibility of secondary infection.