Palivizumab has proved effective in reducing hospitalization rates because of respiratory syncytial virus in vulnerable groups. In Argentina its administration is not universal because of high costs. We made a cohort study and enrolled 159 children who met the American Academy of Pediatrics recommendations but did not receive palivizumab; 26% required hospitalization for respiratory syncytial virus infection. Siblings and bronchopulmonary dysplasia were associated with higher hospitalization. For high-risk patients, one averted hospitalization was associated with costs of U.S. dollars (USD)13, 198 [number needed to treat (NNT): 4.5].