OBJECTIVE: In Japan, measles vaccine coverage is lower than 80% nationwide. As a result, the number of measles case is estimated about 100,000-200,000 a year. In this study, we performed cost-benefit analysis between the cost of vaccination and the cost of treatment of measles. Although cost effectiveness analysis including cost-benefit analysis of vaccination is extensively performed (e.g. influenza), it is not carried out concerning measles at all. This research is unique in this point of view. METHODS: We conducted chart investigation of 291 measles patients (171 outpatient cases and 120 hospitalization cases) in one hospital from July 1997 to September 2001. Among them, medical expenses were calculated about 121 samples of outpatients and 112 inpatients which are considered to be appropriate for the contents of medical treatment. At the same time, we estimated opportunity cost from the employment situation of the parents of the child patients from the chart and the interview. Loss profits were taken into consideration about death cases or the critical sequelae. RESULTS: Medical expenditure in outpatient cases was about 120,000 yen on average, while it was 300,000 yen for hospitalization cases. The opportunity cost was far exceeded medical expenses. Benefit Cost ratio (BCR) was 2.5, when the base case was set up and was presumed. In the result of sensitive analysis of BCR, it ranged from 2.3 at a minimum to about 5 at the maximum. Discussion In the preceding research on the BCR analysis of vaccination, it is well-known that BCR is 1.4 for hepatitis B vaccine for infants, 1.93 for influenza vaccine for pre-school children, and 1.81 for influenza vaccine for healthy adults. When compared with these research, the result of this research shows the validity of a measles vaccine strongly. CONCLUSION: We conclude that measles vaccination is excellent method of prevention from the viewpoint of cost-benefit analysis.