Respiratory syncytial virus (RSV) has been increasingly recognized as an important cause of serious respiratory illness in some adult populations, including those with underlying cardiopulmonary diseases. However, the precise incidence and the clinical impact of RSV in this group are unknown. Therefore, the incidence and clinical impact of RSV infection in persons with chronic obstructive pulmonary disease (COPD) and congestive heart failure (CHF) who reside in the community were prospectively evaluated over two consecutive winters in 134 persons. Eight RSV (incidence of 4.3 per 100 subject-winters), 13 influenza A (incidence of 7.0 per 100 subject-winters), seven rhinovirus, nine coronavirus, and two parainfluenza virus infections were identified. The clinical illnesses associated with RSV and influenza A virus were similar, causing both upper and lower respiratory signs and symptoms. The clinical impact was significant as three of eight RSV-infected subjects were hospitalized compared with six of 13 influenza A-infected persons and zero of seven rhinovirus-infected persons.