Statement of Problem:Recurrent aphthous stomatitis (RAS) is a common oral disorder that despite extensive researches, the etiology of this phenomenon is still unknown. Because this phenomenon has been observed more often in families than in individual cases, genetic influence has been investigated in most researches.
Purpose: The aim of the present study was to evaluate the association between Human Leukocyte Antigen (HLA) and aphthous stomatitis more precisely.
Materials and Methods: in this study, 60 patients with RAS were examined for HLA-A and HLA- B types and 37 of them were examined for HLA- DR and HLA-DQ types. The results were compared through Fisher test with those of 25 healthy control subjects, aged more than 30 years.
Results: A significant decrease in the frequency of some antigens such as HLA-DQW 3 and HLA-A 26 in subjects with RAS was observed. Therefore, according to the results of this study, these antigens were considered as resistant antigens to recurrent aphthous stomatitis. In contrast, there was no significant increase in the frequency of any HLA antigens in the test group, compared to the control group. This finding is in contrast with the multiple reports about Behcet's disease. (Because a high frequency of HLA-B 51 has been
found in Behcet's syndrome.)

Conclusion: According to the findings of this study, it is suggested that the pathogenicity of aphthous ulcerations in Behcet's disease and recurrent aphthous stomatitis is not the same. However, further studies are necessary to prove this theory.