Behçet's disease is an immune-mediated vasculitis affecting both small and large vessels. Small-vessel vasculitis is the pathological basis of the multiorgan involvement that results in protean clinical features. However, relapsing aphthous ulcers in the mouth are considered the clinical hallmark and are often also observed over the genitalia. Both manifestations, in association with uveitis, form the typical clinical triad. In addition, skeletal muscles, joints, gastrointestinal, cardiopulmonary, and central nervous systems can be involved. Heterogeneity in incidence, clinical manifestations, course, and severity are observed according to ethnic background. The natural course is chronic with relapses and remissions, gradually abating over the years, but the illness can also be life or sight threatening. Its origin and cause are still obscure: genetic, infectious, environmental, and immunological factors have been proposed. Owing to the lack of a specific test, diagnosis still relies on recognition of the typical clinical pattern. Treatment usually includes corticosteroids and immunosuppressive drugs. A better understanding of the pathogenesis will hopefully improve both diagnosis and therapy. In addition, the development of tests aimed at monitoring disease activity and response to therapy is certainly desirable.