Background: Hemophilia is the most frequent severe hereditary hemorrhagic disease due to deficiency of coagulation factors VIII (Hemophilia A) or IX (Hemophilia B) in plasma. We aimed to identify patients with hemophilia in Kermanshah, Iran and assess the incidence of inhibitors in this population and its associated factors. Methods: This study was conducted on patients with hemophilia A and B admitted in hospitals of Kermanshah city, referred to coagulation laboratory of Kermanshah blood transfusion organization. Variables including age, sex, family history of the patients in terms of history of hemophilia and inhibitor formation, development of inhibitor in patients, age at starting the treatment, blood group, severity of hemophilia, average of factors received per month and liver disease were assessed in patients. Results: Of 123 patients with hemophilia A, 119 (96.7%) were men. The mean±SD age of patients with hemophilia A was 25.9±15.74 years. Only five men had developed factor VIII inhibitor. Of 25 patients with hemophilia B, 24 (96%) were men with a mean±SD age of 21.7±15.71 years. Factor IX inhibitor was not detected in any patient. There was no association between incidence of inhibitors and age at the onset of the treatment, family history of hemophilia, blood group, severity of hemophilia, average of received factor per month and liver disease. However, a positive association between incidence of inhibitors and family history of inhibitors was found (P<0.05). Conclusion: Association between family history of inhibitor and incidence of inhibitor formation in hemophilic patients was a new finding. Therefore this outcome and genetic evaluation of these for finding relevant mutations should be considered.