Background: The strong association of Behcet’s disease with HLA-B5 antigen has been observed in several ethnic groups from Middle East to Far East. Objective: To evaluate the frequency and association of HLA-B5 and also likelihood ratio of involvement in Behcet’s disease in a group of Iranian patients. Patients and Methods: HLA-B5 antigen typing was performed by serologic method in 56 patients with Behcet’s disease (Diagnosed by International Study Group Criteria) and 71 cases with seronegative diseases as control group. The difference in frequency and association between HLA-B5 antigen and Behcet’s disease was evaluated by chi-square test and phi-test. Results: The phenotype frequencies of HLA-B5 antigen in Behcet’s disease patients and control group were 66% and 26% respectively (X=19.62, P=0.0001). The association of HLA-B5 antigen phenotype with Behcet’s disease was strong (Phi=0.39, P=0.0001). The likelihood ratio was 20:1 for HLA-B5 antigen positivity and Behcet’s disease. Gene frequency of HLA-B5 was 46% in Behcet’s disease patients and 14% in control group. Conclusion: This study revealed a strong association of HLA-B5 antigen with Behcet’s disease in Iranian patients.