It has recently been claimed that some of the symptoms in patients with Behcet's disease (BD) can be activated after the patient has stopped smoking. In this study we investigated the effect of smoking on the symptoms of Behcet's disease. Fifty asymptomatic current smokers (CS) who promised to stop smoking (group 1) and 60 current non-smokers (NS) (group 2) (21 of them ex-smokers) with ED were examined at the beginning and a week later for the presence of symptoms of ED. Forty-seven of the 50 CS completed the study. Oral aphthous ulcers were observed in 31 (65.9%) of them at the end of the study period. Besides oral aphthous lesions, genital ulcers were detected in two and erythema nodosum in two other patients. Only 15 (25%) group 2 patients developed oral aphthous ulcers during the study period. The difference between the frequencies of oral aphthous lesions in these groups was significant (p=0.0002). We concluded that cessation of cigarette smoking can activate the mucocutaneous symptoms, especially oral aphthous lesions, in patients with BD.