From 1 November 1992 through 1 May 1993 and from 1 November 1993 through 1 May 1994, we conducted a prospective surveillance study at the University of Texas M.D. Anderson Cancer Center (Houston) to evaluate the role of community respiratory virus infections in hospitalized adult bone marrow transplant (BMT) recipients, Respiratory secretions were obtained from all adult BMT recipients with acute respiratory illnesses. During these two winters, a community respiratory virus was isolated from 37 (36%) of 102 patients and 30 (26%) of 115 patients, respectively. Approximately half (49%) of these infections were due to respiratory syncytial virus (RSV); the remainder were due to influenza virus (18%), picornaviruses (18%), parainfluenza virus (9%), or adenovirus (6%). Fifty-eight percent of these infections were complicated by pneumonia, with an associated mortality of 51%. The pneumonias that complicated RSV infection were almost exclusively viral in origin and were associated with a mortality of 100% if not treated promptly with antiviral agents. In contrast, many of the pneumonias that complicated the other viral infections, such as influenza, appeared to be either self-limited viral pneumonias or secondary bacterial or fungal pneumonias. Community respiratory viruses are frequent causes of acute respiratory illnesses in adult BMT recipients hospitalized during the winter and are associated with substantial morbidity and mortality.