Behcet's disease (BD) is classified among vasculitides. There are actually five nationwide surveys of BD: Iran, Japan, China, Korea, and Germany. Among case series, four are on more than 200 cases (Turkey, Morocco, Tunisia, and UK). BD was classically seen around the Silk Route. Now, it is seen everywhere. The male to female ratios were, respectively (in nationwide surveys), 1.19, 0.98, 1.34, 0.63, and 1.40 to 1. The mean age at onset was 26.2, 35.7, 33.8, 29, and 26 years. Major manifestations were seen, respectively, in nationwide surveys: mucous membrane (oral aphthosis in 97%, 98%, 98%, 99%, and 98%; genital aphthosis in 65%, 73%, 76%, 83%, and 64%); skin manifestations (pseudo-folliculitis in 57%, N/A, 31%, N/A, and 62%; erythema nodosum in 22%, N/A, 38%, N/A, and 42%; ocular manifestations in 55%, 69%, 35%, 51%, and 53%). Minor manifestations were seen, respectively, in nationwide surveys: joint manifestations in 33%, 57%, 30%, 38%, and 53%; neurological manifestations in 9%, 11%, 6.5%, 4.6%, and 11%; gastrointestinal manifestations in 7%, 15.5%, 9%, 7.3%, and 12%; vascular involvement in 8.9%, 8.9%, 7.7%, 1.8%, and 13%; pulmonary manifestations in 0.3%, N/A, 2.2%, N/A, and 3.6%; cardiac manifestations in 0.5%, N/A, 4%, N/A, and 3.2%. Laboratory tests are not useful except the pathergy test, which was positive in 54%, 44%, N/A, 40%, and 34% of cases. ESR was normal in many patients. Diagnosis is based upon clinical manifestations. The International Criteria for Behcet's Disease (ICBD, 2006) may be of help, having a sensitivity of 98.2% and a specificity of 95.6% in Iranian patients.