The acne lesions characteristic of Behçet's syndrome are not sterile and are commonly observed in combination with arthritis. The two main nodular skin lesions--superficial thrombophlebitis and erythema nodosum--are equally frequent, and rather difficult to distinguish. Superficial thrombophlebitis is usually observed in combination with thrombosis in large veins, and thrombosis of the large veins usually clusters with dural sinus thrombi, which make up approximately 20% of all central nervous system (CNS) lesions of Behçet's syndrome. The remaining CNS lesions are parenchymal, mainly located in the brainstem, and associated with a graver prognosis than dural sinus thrombi. The presence of clinical clusters indicates that there are at least two pathogenetic pathways in Behçet's syndrome: a reactive arthritis pathway and a thrombophilia pathway. Research into the pathogenesis of Behçet's syndrome has shown that the most consistent genetic marker of Behçet's syndrome is HLA-B51; however, the genetic association of this true-to-form 'complex' disorder with HLA-B51 is only 20%, and a whole-genome study showed associations with 16 different loci. The severity of Behçet's syndrome and the mortality associated with it tend to decrease with time, and there is no associated increase in incidence of atherosclerosis. Although treatment of skin-mucosa manifestations, eye disease and pulmonary artery aneurysms has improved significantly in the past decades, the treatment of CNS lesions and thrombophilia are still problematic.