Abstract: Behcet's disease (BD) is not ran in Iran. The annual incidence is around 345 patients for a population of 60 millions. The male/female ratio is 1. 13. The mean age at the onset of the disease is 26.2+9.7 years (CI at 95%=0 .4). The prevalence of clinical signs were as follow: Mucous membrane lesions 96%+0.7 (oral aphthosis 95.7%, genital aphthosis 64%); skin lesions 74%±I.5 (pseudofolliculitis 66%, erythema nodosum 23%): ocular lesions 59%+1.7 (anterior uveitis 45%, posterior uveitis 46%, retinal vasculius 32%), articular manifestations 41%+1.7 (arthralgia 20%. monoarthritis 9%. oligoarthntis 19%, ankylosing spondylitis 1.7%); neurological manifestations 3.5%+0.3 (central 3.3%, peripheral 0.2%); vascular involvement 9.7%+ 0.5 (deep vein thrombosis 7%, superficial phlebitis 2.2%, large vein thrombosis 1.2%. arterial aneurysm 0.3%); gastrointestinal manifestations 9%+1 (dyspepsia 3.6%, acute abdomen 2%, rectorrhagia 1%, diarrhea 2.1%); cardiopulmonary involvement <1%; orchi-epididymitis in 11% of men. In paraclinical tests: Pathergv test was positive in 61%, HLA-B5 in 55%, HLA-B27 in 9.6% and false positive VDRL in 2% of patients. Abnormal urine sediment was seen in 11% but renal biopsy was done only in 12 patients (WHO type II: 2 cases. type III: 6 cases, type IV: 4 cases. amyloidosis: 1 case). Comparison of these data with the nationwide survey of BD in Japan showed a 5 to 15% higher prevalence of the majority of the symptoms in Japan (including oral and genital aphthosis, skin and ocular lesions, articular and gastrointestinal manifestations). The prevalence of orchi-epididymitis and positive pathergy test were lower (p<0.000001 ), while the prevalence of vascular involvement was the same (p=0.70). This difference may be due to the exclusion of milder cases in the Japanese survey (hospital based survey, diagnosis based on the Japan criteria) However a different genetic background and/or an environmental factor may not be excluded.