Community-acquired respiratory virus (RV) infections are an important cause of disease in immunocompromised adults with cancer. To investigate the viral etiology, incidence, clinical presentation, and outcome of RV infections in an outpatient cohort of adult bone marrow or peripheral blood stem cell transplant (SCT) recipients, we monitored 62 outpatient volunteers from January 1 to April 30, 2001. A nasopharyngeal aspirate was collected from subjects when they reported new respiratory symptoms and tested for RV (influenza A, influenza B, human parainfluenza 1-3, adenovirus, and respiratory syncytial virus) by culture and reverse transcription polymerase chain reaction (RT-PCR) assay. Of 62 subjects enrolled, 27% had received allogeneic SCT and 45% were within 1 year of their transplant. In all, 35 participants (56%) reported 37 episodes of respiratory symptoms. Of the 37 specimens tested, five (14%) were positive for RV by culture and 20 (54%) were positive by RT-PCR. Only six patients with RV infections developed lower respiratory tract illnesses; these patients had received either autologous or allogeneic transplants and developed illnesses between 41 and 2666 days post transplant. Although RV infections were common in SCT outpatients during the RV season, most participants had upper respiratory tract infections, which resolved without the need for hospitalization.