OBJECTIVE: To investigate the clinical, laboratory and radiologic characteristics of arthritis presented as initial manifestation in patients with Behcet's disease. METHODS: We retrospectively reviewed medical protocols, laboratory and radiologic findings in 33 patients with Behcet's disease. Evaluation was made out at diagnosis and included age, sex, duration and onset pattern of arthritis, involved joint, and laboratory findings included erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), anti-nuclear antibody (ANA), rheumatoid factor (RF), and HLA type. RESULTS: In 33 patients (7 males and 26 females), mean age was 34.4+/-9.4 years, and duration of arthritis was 34.1+/-37.9 months. The frequency of involved joint was as follows ; 58% in knee, 33% in proximal interphalangeal joints, 27% in wrist, and 24% in ankle. The pattern of involvement was oligoarticular in 18 patients (55%), polyarticular in 9 patients (27%), and monoarticular in 6 patients (18%). Monoarticular pattern was more frequent in younger patients (< or =35 year-old) than older patients. ESR and CRP were elevated in 17 (53%) and 8 patients (24%), respectively. Radiologic examination of the involved joint was normal in 93% of patients. CONCLUSION: In patients with Behcet's disease diagnosed by arthritis as initial manifestation, the most commonly involved joint was knee and the most common pattern of involvement was oligoarticular.