OBJECTIVE: To investigate the occurrence of nosocomial respiratory syncytial virus (RSV) infections and to compare their clinical features with those of community-acquired RSV infections. DESIGN: Retrospective. METHOD: Data were collected from the medical records of children younger than 12 months with RSV infection in the Department of Pediatrics of Sophia's Children's Hospital, Rotterdam, the Netherlands, in October-March 1992/'95. The diagnosis of 'RSV infection' was confirmed by a direct immunofluorescent assay and/or a viral culture on materials obtained from nasopharyngeal washes. A nosocomial RSV infection was defined as an infection which occurred more than 5 days after hospital admission for any underlying disease. RESULTS: During the 3 RSV seasons 1260 children were admitted. Of these 34 (2.7%) developed a nosocomial RSV infection. The number of nosocomial RSV infections decreased over the study period. At the department including the outpatient clinic 232 children were seen with a community-acquired RSV infection. Children with a nosocomial infection differed from children with a community-acquired infection only with regard to birth weight (2.5 kg versus 3.0 kg), cough (65% versus 92%) and feeding problems (100% versus 69%). Four children had bronchopulmonary dysplasia and nosocomial RSV infection; these required mechanical ventilation. CONCLUSION: The number of nosocomial RSV infections decreased over 3 years. The severity of nosocomial RSV infections was comparable with that of community-acquired RSV infections.