Infection with hepatitis C virus (HCV) is frequently observed among Japanese hemophilic patients, and critical hepatic diseases arising from HCV infection have become a major cause of death. Therefore, we tried to estimate the benefits of the interferon therapy among 1,241 hemophilic patients with chronic hepatitis. We used the viral genotype and the RNA concentration as two predicting variables for the efficacy of the interferon therapy, and assumed a binomial logistic regression model. The missing data of the patient’s viral genotype and RNA concentration were substituted by random numbers simulating the actual observed distribution. By repeating the computation 1,000 times using different sets of random numbers, we estimated the number of sustained viral responders (SVR) resulting from the therapy. We observed certain changes in the estimated number of SVR by changing the dependence assumption of therapeutic efficacy on the predicting variables. In the most optimistic scenario, the estimated number for SVR was 692 ± 17 (55. 8 ± 1. 4%), while it was 461 ± 16 (37. 1 ± 1. 3%) in case of the most pessimistic scenario. The effect of the missing data on the estimates was not large. Therefore, these estimates will be helpful for making a prospective evaluation of the survival benefits coming from the spread of the interferon therapy.