Abstract: No fewer than five sets of diagnostic criteria for Behcet's disease are currently in use. The International Study Group have therefore undertaken an extensive study of existing criteria and have developed recommended new international criteria based on the collection of data from 914 patients with Behcet's disease and 308 controls, of whom 886 (97%) and 97 respectively had mouth ulceration. It is recommended that these new criteria should replace the existing criteria sets although further studies are required to evaluate their performance in new patient groups.