We asked whether pediatric renal transplant recipients, subgrouped by age, differed in the percentage and number of hospital readmissions and in the incidence of infectious complications post transplant. Between 1 August 1985 and 31 October 1993, a total of 164 patients < 18 years of age underwent primary transplants, with cyclosporine-based immunosuppression, at the University of Minnesota. The percentage of readmissions (P = NS), the mean number of readmissions (P = NS), and the length of hospital stay during readmissions (P = NS) did not differ significantly among age groups. The overall incidence of acute rejection was greater in those > or = 2 years than those < 2 years (P = 0.002), and in living donor recipients > or = 2 years versus those < 2 years (P = 0.02). The incidence of bacterial infection (< 2 years, 87%; 2-5 years, 72%; 6-12 years, 51%; 13-17 years, 40%) was greater in younger recipients (P = 0.0001). The most common bacterial infection in recipients < or = 5 years was Clostridium difficile-associated diarrhea; in those > 5 years, urinary tract infection. The overall incidence of viral infection did not differ among groups (P = NS). The most common viral infection in recipients < or = 5 years was varicella and those > 5 years, cytomegalovirus infection. Risk factors for infection in the first 6 months post transplant included age < 2 years and Solu-Medrol treatment for acute rejection. In conclusion, young recipients < 2 years of age at the time of transplant are at a higher risk for bacterial infection post transplant.