Objective.To provide information on the use and outcomes of palivizumab prophylaxis in children at high risk of serious respiratory syncytial virus (RSV) infection.Design.Observational, prospective, longitudinal, multicenter study.Setting.Eighteen hospitals and pediatric clinics located in six provinces across Canada.Patients.Infants enrolled in the palivizumab Special Access Programme of Canada’s Therapeutic Products Programme throughout the 1999 to 2000 RSV season. Most were premature infants born at ≤32 weeks of gestation and/or had bronchopulmonary dysplasia.Methods and main outcome measures.Neonatal and demographic data were recorded for each subject. The parent/caregiver was contacted on a monthly basis until the end of the RSV season to obtain information on palivizumab utilization and compliance as well as incidence and severity of respiratory infections.Results.There were 444 evaluable subjects who each received 1 to 7 injections of palivizumab for a total of 1702 doses from September 1999 to April 2000. Most subjects received 5 injections with high compliance. Prophylaxis was discontinued in 2% of children. There were 116 clinical events or hospitalizations involving respiratory tract infections reported in 91 children. Eighty-six of these were managed in an outpatient setting, and 30 required hospitalization. The estimated incidence of hospitalization for RSV-positive lower respiratory tract infections (LRTIs) was 2.4%. Hospitalization for RSV LRTI occurred more often in children with bronchopulmonary dysplasia (6.0%) than in those with prematurity only (1.6%).Conclusions.This study demonstrates that prophylaxis with palivizumab during the RSV season was associated with a low rate of hospitalization for RSV-positive LRTIs. Palivizumab was well-tolerated, and compliance was high. The findings confirm the results of the major randomized clinical trial of palivizumab and demonstrate the safety and effectiveness of RSV prophylaxis.