Behçet's disease (BD) is a chronic, relapsing, systemic vasculitis with unknown etiology. During the progression of the disease, gastrointestinal involvement can be observed. The aim of this study was to find out the predictive value of the sucrose permeability test in detecting gastrointestinal mucosal damage in BD. Twenty-six male Behçet's patients and 21 age- and sex-matched controls were enrolled in the study. Seventeen patients had active disease, while nine did not. Active disease was defined as having elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels or at least two of the diagnostic criteria in the previous month. Patients and controls were investigated with the upper gastrointestinal permeability test. Of all the patients, 25 were investigated endoscopically. The urine sucrose levels were significantly higher in patients than in the control group (P = 0.0001) and in patients with active disease than those with inactive disease (P < 0.0001), while urine sucrose of patients with inactive disease and the control group did not differ. The endoscopic findings were not specific to BD. Active and inactive BD had similar endoscopic findings. Increased upper gastrointestinal permeability was established in patients with BD. This increased permeability was not related to a specific gastrointestinal BD lesion. Further studies with larger series must be performed in order to determine the value of the sucrose permeability test in detecting mucosal involvement in BD.