There are no specific diagnostic laboratory tests for BehÇet's disease. Diagnosis relies on proper history-taking and typical clinical manifestations. To provide more objectivity to the diagnosis, several diagnostic criteria have been introduced including one major set of guidelines by the International Study Group for BehÇet's Disease (ISGBD) in 1990 which has made a significant contribution, although some disagreements exist in interpretation. Based on this criteria, recurrent oral ulceration is an obligatory manifestation for the diagnosis of BehÇet's disease; however, some data indicates it is not a requirement for the diagnosis. In this article the author critically reviews different accepted diagnostic criteria or classifications of BehÇet's disease and gives recommendations for a more thorough diagnosis.