The aetiopathogenesis of Behcet's disease is still not known. In the light of current knowledge, the most likely hypothesis seems to be that of an autoimmune reaction set off by viral, bacterial or other antigens. The reaction may manifest itself in the vascular system, and cause vasculitic conditions in genetically susceptible subjects. The existence of a constitutional susceptibility factor would seem to be confirmed by the high and significant incidence of determinant histocompatibility antigens: HLA-B5 in Japan and in Mediterranean countries, HLA-A2 and HLA-A28 in Great Britain and the United States. Corticosteroids are most commonly used to treat the disease; immunosuppressants are also recommended--possibly in association with corticosteroids. Three personally observed cases of Behcet's disease are reported. The first was an example of the disease in its complete form (oral and genital aphthae, ocular lesions); the second case incomplete (no genital aphthae); and the third characterised by severe neurological involvement (neuro-Behcet).