Seventy seven patients, thirteen younger than 20 years of age, were followed up prospectively for the first three months after renal transplant for evidence of infection and illness due to cytomegalovirus (CMV). Thirty-two developed reactivation of latent CMV and 29 did not develop any CMV infection and wn, five had pneumonia, and four underwent nephrectomy. Of these, 16, eleven received a kidney from a parent, whereas of the other 61 patients, five received parental kidneys (P less than .001). Hence, CMV seronegative individuals who received a kidney from a CMV seropositive parent developed clinical illness and sometimes lost the allograft.