OBJECTIVES: Respiratory syncytial virus infection (RSV) is a leading cause of rehospitalization in high-risk infants such as premature and bronchopulmonary dysplasia (BPD). Palivizumab is effective for prevention of serious RSV illness in such high-risk infants but cost-effectiveness of palivizumab in Japan has not been reported. The aim of this study was to assess the cost-effectiveness of palivizumab for prevention of rehospitalization due to RSV infection in premature infants and such with BPD in Japan. METHODS: A decision tree was constructed to estimate the cost-effectiveness of palivizumab in Japan. Probabilities of rehospitalization, death and asthma as sequelae were obtained from published studies. Drug cost of palivizumab was set based on the Japanese drug price list. Other cost parameter was obtained from published literature in the Japanese setting. We employed a payer's perspective and only considered direct medical cost. The discount rate employed was 3%. RESULTS: The expected cost was $7,665 (JPY 896,752) in the palivizumab and $328 (JPY 38,373) in the no prophylaxis, respectively. QALYs was 30.392 in the palivizumab and 30.200 in the no prophylaxis, respectively. The incremental cost-effectiveness ratio (ICER) of palivizumab was $38,312 (M JPY 4.48). Sensitivity analyses showed that the results are more sensitive to the hospitalization rate of palivizumab and less sensitive to the cost of hospitalization and asthma. CONCLUSION: ICER of palivizumab in Japan was similar to results in other countries. This study suggested that Palivizumab for prophylaxis of rehospitalization due to RSV infection in premature infants and such with BPD appeared to be cost-effective in Japan.