Abstract: There are only two nationwide surveys of Behcet's Disease (BD) in the world, one from Japan and one from Iran. The comparison of the two surveys is interesting because the populations are racially different, although they share same genetic background via the invasion of Iran by Turk tribes (from the northem part of China) in the 10 th and 13 th century. The annual incidence of BD in Iran is 350 new patients for a population of 60 millions, which may correspond to a prevalence of 1 BD for 6000 inhabitants.The male/female ratio is 1.16. The mean age at the onset of the disease is 26.2 + 9.7 (Cl at 95% = 0.4). The incidence of clinical symptoms were as follow: Mucous membrane manifestations: 95.8% + 0.7 (oral aphthosis: 95.5%, genital aphthosis: 64%). Skin manifestations: 74% + 1.6 (pseudofolliculitis: 67%, erythema nodosum: 23%, other skin lesions specially skin aphthous lesions: 5%). Ocular manifestations: 61% + 1.8 (anterior uveitis: 47%, posterior uveitis: 48%, retinal vasculitis: 32%). Joint manifestations: 43% + 1.8 (arthralgia: 22%, mono-arthritis: 10%, polyarthritis: 20%, ankylosing spondylitis: 1.8%). Neurological manifestations: 3.2% + 0.7 (central manifestations: 3%, peripheral manifestations: 0.2%). Gastro-intestinal manifestations: 4.2% + 0.7 (acute abdomen: 2.1%, proctorrhagia: 0.7%, chronic recurrent diarrhea 2.1%). Orchiepididymitis: 6.2% + 0.9. Phlebitis: 7.1% + 0.9. Large vein thrombosis: 1% + 0.4. Arterial thrombosis: 2 cases. Aneurysm: 6 cases (0.2% + 0.2). Pathergy test was positive in 62%, HLA-B5 in 55% (34% in normal population), HLA-B27 in 10% (4% in normal population), false positive VDRL in 2.3% of patients. Abnormal urine sediment was seen in 7.6% of patients. Renal biopsy was done in 11 patients for persistent high proteinuria: WHO type 2:1 case, type 3:6 cases, type 4: 4 cases, amyloidosis: 1 case. The comparison between Japan and Iran surveys demonstrates minor differences: Higher incidence in Japan for genital aphthosis (+10%), skin manifestations (+13%), ocular symptoms (+8%), joint manifestations (+14%), G.I. manifestations (+11%), and neurological manifestations (+8%). The Japanese patients were hospital treated patients, excluding therefore mild cases. This may explain the higher incidence of symptoms in the Japan Survey.