Patients maintained on chronic hemodialysis have an increased incidence of spontaneous bleeding from various parts of the body. In this paper we describe 5 patients who developed spontaneous retroperitoneal hemorrhage. All patients were receiving anticoagulants (Coumadin and/or heparin) at the time of bleeding. Clinically, retroperitoneal hemorrhage was evident in the interdialytic period. Presenting symptoms and signs included sudden and progressive onset of pain in the abdomen, flank, back, thigh or hip associated with a drop in blood pressure and hematocrit in the absence of obvious blood loss. Subsequently ecchymosis, swelling and/or mass were observed. Abdominal X-rays showed absent psoas shadows. Treatment included blood transfusions, discontinuation of Coumadin and/or heparin, the use of regional heparinization for hemodialysis and occasionally peritoneal dialysis. Surgical exploration was not required in any case and all 5 patients recovered. Anticoagulation therapy and platelet dysfunction may be contributory causes.