The role of respiratory viruses in severe complications following bone marrow transplantation was examined in a survey of selected transplant centers in Europe belonging to the European Group for Blood and Marrow Transplantation. Information was collected on 57 cases of infections with respiratory viruses, including adenoviruses. In two centers that had conducted prospective studies of bone marrow recipients with respiratory symptoms, the frequency of these infections was 7.1% and 4%, respectively. The severity of these infections varied. Pneumonias caused by respiratory syncytial virus and adenovirus were associated with mortality rates of 60% and 75%, respectively, whereas pneumonia caused by parainfluenza had a mortality rate of 20%. Influenza infections progressed to fatal pneumonia in 17% of cases. Results of antiviral therapy varied. As the results of our survey showed, respiratory virus infections are not infrequent after bone marrow transplantation and are associated with significant morbidity and mortality.