Behcet's syndrome was recorded as a clinical rarity until recently, chiefly among Japanese or Turkish patients. More recently, it has been recognized as an entity that is seen worldwide, defined as oculomucocutaneous syndrome with many systemic features, including thrombotic involvement of the large veins and the major arteries, demyelinating disease of the CNS, ulcerative disease of the gastrointestinal and genitourinary tracts, and sparing, in selected patients, virtually no organ system. A tenuous association with HLA-B5 has been identified, chiefly in propositi from the Middle East, North Africa, and northern Japan, although this association seems not to hold in surveyed patients from the midlands of England and the northern tier of the United States. The cause remains obscure, but some relationships to trace metals and to immunologic features have been inferred. The regular administration of colchicine and the use of transfer factor both have seemed to alter the course in some