Twenty seven children were followed up prospectively after renal transplant for evidence of infection and illness due to cytomegalovirus (CMV), Epstein-Barr virus (EBV) and varicella zoster virus (VZV). Virus shedding and serological status were tested at transplant day, biweekly for two months, monthly for six months and trimestrialy thereafter. Determinations were done by complement fixation test. CMV isolation was established by microscopic examination of urinary cultures. Primary infections were objetivated in 27 cases (18 CMV, 1 EBV, 8 VZV) and reinfection in 3 (2 CMV, 1 VZV). Irreversible allograft rejection related to infection was disclosed in 2 patients (1 primary CMV infection, 1 VZV reinfection). Renal function impairment occurred only with CMV (6 primary and 1 secondary infections). One patient died with CMV over infection.