Abstract: Objectives: Behcet's disease (BD) is a multi-system disease. We present here the various clinical aspects of BD based on the data of 4586 Iranian patients. The male to female ratio was 1.17/l. The mean age at the onset of the disease was 26 yr (SD:9.6, CI:0.3). The mean disease duration was 9 yr (SD:7), and the mean follow up time was 3 yr (SD:3.8). As the first manifestation of the disease oral aphthosis was seen in 80% (CI:1.2), genital aphthosis in 10% (CI:0.9), Ocular involvement in 10% (CI:0.9), joint manifestations in 5% (CI:0.6) and other manifestations in 8% (CI:0.8). The prevalence of clinical signs were as follow: Mucous membrane lesions in 96.8% (CI:0.5) cases, oral aphthosis in 96.5% (CI:0.5), genital aphthosis in 65% (CI:1.4); skin lesions in 71% (CI:1.3), pseudofolliculitis in 63% (CI:1.4), erythema nodosum in 22% (CI:1.2); ocular lesions in 56% (CI=1.4), anterior uveitis in 41% (CI:1.4), posterior uveitis in 45% (CI:1.4), retinitis in 31% (CI:1.3); joint manifestations in 35% (CI:1.4), ankylosing spondylitis in 1.5% (CI:0.4); vascular involvement in 8.6% (CI:0.8), CNS lesions in 3.1% (CI:0.5); GI involvement in 8% (CI:1.4); pulmonary and cardiac involvement each in <1% (CI:0.3); orchi-epididymitis in 11% (CI:1.2). In Laboratory tests: Pathergy test was positive in 59% (CI:1.4), HLA-BS in 54% (CI:1.5), HLA-B27 in 10% (CI:0.9), high ESR in 54% (CI:1.5) and urinary abnormalities in 10% (CI:0.9). Positive family history for BD was present in 6% (CI: 1). Juvenile form of the disease was seen in 4.6% (CI:0.6). The most sensitive criteria in our patients was classification tree (97%, CI:0.5). The sensitivity of other criteria were as follow: Mason & Barnes 68% (CI:1.3), O'Duffy 73% (CI:1.3), ISG 83% (CI:1.1), Dilsen 87% (CI:1), Japan 88% (CI:0.9), Iran 93% (CI:0.7).