Based on a description of the disease in 12 patients (six German, five Turkish and one Yugoslav) the symptoms and diagnostic criteria of Behçet's syndrome are explained. Regional differences in sex distribution, differences in the symptomatology of female and male patients, severe vascular complications, and lymphoproliferative disorders in the advanced stages receive particular mention. In the absence of specific laboratory findings, diagnosis and assessment of disease activity depend primarily on clinical criteria. The present conception of the etiology yields several therapeutic regimens, though their efficacy is difficult to evaluate due to spontaneous remissions and exacerbations.