After renal transplantation, hemolytic uremic syndrome (HUS) may occur as recurrent disease or de novo. Here, we describe the de novo occurrence of HUS immediately after the onset of primary cytomegalovirus (CMV) disease in two renal allograft recipients. Patient no. 1 had primary CMV disease with biopsy-proven CMV esophagitis 2 months after transplantation. Patient no. 2 experienced primary CMV disease with fever and leukopenia 8 years after transplantation. Both patients were treated with intravenous ganciclovir. Both patients developed HUS with biopsy-proven thrombotic microangiopathy in the renal allograft only a few days (3 to 5 days) after the onset of CMV disease. The short interval between the onset of CMV disease and HUS, as well as the parallel course of CMV viremia and HUS in both patients, indicate there may be a pathophysiological link between both diseases. However, because antiviral therapy with ganciclovir was started before the onset of HUS in both patients, we cannot definitely rule out that HUS was triggered by ganciclovir.