The aims of this study were to determine the presence of respiratory syncytial virus (RSV) and to assess the clinical features of the disease in infants with acute low respiratory tract infection hospitalized at pediatric intensive care units (PICU) of two university teaching hospitals in São Paulo State, Brazil. Nasopharyngeal secretions were tested for the RSV by the polymerase chain reaction. Positive and negative groups for the virus were compared in terms of evolution under intensive care (mechanical pulmonary ventilation, medications, invasive procedures, complications and case fatality). Statistical analysis was performed using the Mann Whitney and Fisher's exact tests. A total of 21 infants were assessed, 8 (38.1%) of whom were positive for RSV. The majority of patients were previously healthy while 85.7% required mechanical pulmonary ventilation, 20/21 patients presented with at least one complication, and the fatality rate was 14.3%. RSV positive and negative groups did not differ for the variables studied. Patients involved in this study were critically ill and needed multiple PICU resources, independently of the presence of RSV. Further studies involving larger cohorts are needed to assess the magnitude of the impact of RSV on the clinical evolution of infants admitted to the PICU in our settings.