Adenovirus is a common cause of morbidity and mortality after hemopoietic stem cell transplantation in children. Recently the incidence, risk factors, and outcome of such infections have been better defined using improved virologic detection methods, in particular polymerase chain reaction. We have introduced intensive virologic surveillance for adenovirus in our institution including at least weekly polymerase chain reaction testing of blood and stool samples. We report on 71 prospectively monitored transplants, including 40 from unrelated donors. In total, there were 8 cases of invasive adenovirus infection, 3 of whom died. Mortality was less than in previous studies as cases were managed with antiviral chemotherapy and reduction of immune suppression. In fatal cases, there was concurrent difficult graft versus host disease making withdrawal of immune suppression therapy impossible. We describe 2 cases of graft failure in association with adenovirus viremia and its treatment that were successfully managed with further donor cell infusion.