Infections are a major cause of morbidity and mortality after organ transplantation in children. Immunosuppression, surgery, and invasive devices all predispose to infection. A comprehensive pretransplantation evaluation can minimize risks and help anticipate special problems. Appropriate anti-microbial coverage during the perioperative period decreases the risk of infection. Bacteria and fungi are the major causes of infections occurring in the first month after transplantation. The site of infection during this period varies by organ transplanted: liver recipients often have intraabdominal infections, kidney recipients are predisposed to urinary tract infections and perinephric abscesses, and heart recipients often have respiratory tract or sternal wound infections. Viruses play a major role in infections occurring more than 1 month after transplantation, with cytomegalovirus the most significant agent. Other viruses of concern include herpes simplex virus, varicella-zoster virus, several common respiratory viruses, and Epstein-Barr virus with associated lymphoproliferative disorders. Tuberculosis, toxoplasmosis, and Pneumocystis pneumonia also occur later. Appropriate immunization and antimicrobial prophylaxis can help prevent infectious complications after transplantation.