In this prospective study, the incidence of cytomegalovirus (CMV) infection and CMV disease was determined in 175 renal transplant recipients on cyclosporin and low-dose prednisone. CMV infection occurred in 51.4% of the patients, CMV disease in 13.7%. The major manifestations of CMV disease were fever of unknown origin and leukopenia. In the group with CMV infection, there was an increased occurrence of rejection (60% in infected vs 27% in noninfected patients). In most patients (41/54), the rejection preceded the CMV infection. CMV infection did not lead to a decreased graft survival. There was no close time relationship between the onset of clinical symptoms of CMV disease and the laboratory confirmation of CMV infection. A subgroup of patients at risk for the development of severe CMV disease could not be identified.