Among acute respiratory infections (ARIs), respiratory syncytial virus (RSV) is an important pathogen, especially in infants and preschool children. This study focused on RSV epidemiology in a region of southeastern Brazil with a tropical climate. A total of 406 nasopharyngeal secretion samples were taken from children less than five years of age with ARIs. Of these, 114 (28%) were RSV-positive. These samples were found in all age groups, but showed a higher prevalence in newborns. Infection with RSV was identified in 10 of the 12 months of the study period, but the majority (88.5%) of cases occurred from late summer to mid-fall.