Fifty-nine renal transplant recipients with overt CMV disease were treated at the University of Minnesota Health Sciences Center between October 1, 1977 and November 15, 1978. In a group of 141 consecutive transplant patients, the incidence of overt CMV disease was 31%. Fifty-three patients (90%) developed clinical manifestations of CMV disease within 4 months of transplantation, and it was during this time period that overt CMV disease was associated with a significantly increased incidence of transplant nephrectomy and death. Fever was the most common presenting symptom (95% of patients), and overt CMV disease was found to be the single most common cause of fever in all hospitalized transplant recipients. Prolonged fever, diffuse pulmonary infiltrates, gastrointestinal bleeding, pancreatitis, transplant nephrectomy and development of other systemic infections were clinical features used to categorize patients according to disease severity. A number of these features were found to be significantly associated with the diagnosis of overt CMV disease. Twelve patients (20%) developed lethal CMV disease characterized by the presence of most of these features, 6 (10%) had severe disease, 9 (15%) had disease of moderate severity and 32 patients (54%) had mild CMV disease with fever being essentially their only clinical finding. Development of secondary systemic infection was most ominous, and occurred before death in 10 of the 12 patients with lethal CMV disease. The only patients to die with serious bacterial, fungal or protozoan infection during the period of this study had concomitant overt CMV disease. Abnormal liver function tests and leukopenia were common, and the degree of abnormality correlated with the severity of CMV disease. Of the multiple factors analyzed for their influence on the risk of developing overt CMV disease, several factors related to the kidney donor (the relationship of the donor to the recipient, HLA matching and CMV serology) appeared to be most important.