Respiratory syncytial virus (RSV) is a recognised cause of lower respiratory tract infection in infants and young children. It causes severe respiratory disease in preterm infants with or without chronic lung disease. This study, conducted at Waterford Regional Hospital, evaluates the incidence of RSV infection in hospitalised children, its seasonal variation, and effectiveness of its prevention. Thirty eight percent of admitted children with bronchiolitis were RSV positive in the year 1999 November to March is the peak season for this infection. A highly selected group of 7 preterm children with or without chronic lung disease received Palivizumab prophylaxis. Not one of them acquired RSV infection. The high cost of Palivizumab was the main factor for its restricted use. Palivizumab was found to be effective in preventing RSV infection in our study. Since we had a small number of patients, further studies are needed for its economic and judicious use. Respiratory syncytial virus (RSV) is virulent easily transmissible and the most common cause of lower respiratory tract disease in children of less than 2 years of age. Up to 98% of children attending day care will be infected in single RSV season. Between 0.5% and 3.2% of children with RSV infection require Hospitalisation. Approximately 90,000 hospital admissions and 4500 deaths per year were reported in United States. In Ireland 2807 patients were admitted with Bronchiolitis in 1998. Major risk factors for hospitalisation due to RSV are Prematurity, chronic lung disease, congenital heart disease, compromised immunity and age younger then 6 weeks in otherwise healthy children. No effective treatment of RSV positive bronchiolitis beside supportive care in the form of adequate nutrition and oxygen therapy is available. Antiviral therapies such as Ribavirin has not been proved to be effective in RSV infection. Bronchodilators show variable results. Corticosteroids were not found effective. There is no effective vaccine available as yet. There is no proven method for active immunity. Various immunoglobulins are available for acquiring passive immunity against RSV infection. PREVENT study group in Jan. 1997 showed intravenous immunoglobulin (RSV- IGIV) use in reducing 41% to 63% hospitalisation in RSV patients. But RSV-IGIV was not licensed outside the United States because of risk of transmission of blood borne products, difficulty in administration ie. intravenous access, large fluid volume (15 ml/kg), high protein load (750 mg/kg), shortage of supply and need to postpone live vaccine (eg. MMR, varicella). monoclonal antibody Palivizumab was developed for prophylaxis against RSV infection. Clinical safety and efficacy of Palivizumab were demonstrated in IMpact trial published in Sept. 1998. Reduction in hospitalisation up to 55% was noted in this study. It was a pivotal randomised, double blind, placebo controlled phase 3 study conducted in 139 centres throughout Canada, United States and United Kingdom. We looked at our experience in patients admitted with bronchiolitis in Waterford Regional Hospital. We described the outcome of carefully selected Seven children of high risk group for Palivizumab prophylaxis. Its clinical Implications and cost effectiveness was evaluated in this study.