Thirty-two patients with Behcet's syndrome were surveyed clinically, radiologically, and immunologically. HLA antigens were determined in a proportion. The patients were culled from a defined geographical area (Yorkshire) with a population of 5 million. 21 patients satisfied Mason and Barnes's (1969) criteria for major disease. 100% had mouth ulceration, 91% genital ulceration, 66% skin complaints, and 63% arthritis (of the nonerosive type previously documented). 3 patients had gastrointestinal involvement, one of whom had proven Crohn's disease. One patient had psoriasis. One patient had a popliteal artery aneurysm resected and one has since had surgery after the development of a tracheo-osophageal fistula. No sacroilititis was found.