The clinical triad of Behçet's syndrome, ulcers of the oral cavity and genitalia and relapsing iritis was first described in 1937 by Behçet. This entity, originally confined the above triad of symptoms, appears to be a systemic disease manifested by skin lesions, thrombophlebitis, neurologic or visceral symptoms and finally lead to blindness and death. Oral ulceration was found in almost all cases, so the otorhinolaryngologist had important task of early detection and prevention of disease progression. The purpose of this study is to review and clarify the oral lesions in 243 Behçet patients and immunologic aspect who visited out Behçet clinic from Nov. 1983 to Sep. 1984. 1) Behçet's syndrome shows highest incidence in 4th decade female patient. 2) Oral ulceration shows most cases as initial symptom and play an important role for diagnosis of Behçet's syndrome. 3) In type of oral ulceration, minor aphthous ulceration was most common(79.7%). 4) Incomplete type shows highest incidence(39.9%) in classification by Shimizu and mucocutaneous type shows highest incidence(53.9%) in classification by Lehner. 5) Patient group shows decreased active and helper T-cell number and increased B-cell number in comparison to normal control group.