Published data by the Organización panamericana de la Salud shows that Peru's mortality rate from acute respiratory infections (ARI) in infants less than one year of life is second only to Haiti (14,150/100,000). Government data reports shows a marked increase of RSV infections in Peru. "Instituto Nacional de Salud" (Peru's National Institute of Health) reports between January 1st to February 26th 2006, 62% of their positive samples corresponded to RSV. Epidemiological data from Lima-Peru, demonstrates that there is no specific season for RSV infection although some data suggest an increase in RSV activity during cold months (May to September; INS data). Clinical studies show that giving five doses of Synagis (palivizumab) resulted in serum concentrations > 30 ug/mL for >20 weeks. The aim of this post-marketing observational study is to determine the RSV hospitalization rate in high-risk infants who received Synagis (palivizumab) through the Social Security Hospitals in the context of routine clinical practice.