Beh double dagger et's disease (BD) is a multisystemic, chronic inflammatory, relapsing disorder that is characterized by oral/genital ulcerations, ocular, arthritic, vascular, and neurologic involvements. Recent findings suggest the role of increased oxidative stress and insufficient antioxidant defence system in BD pathogenesis. It has been proposed that the increase in phagocytic cell activity by triggering oxidative reactions in various targets such as lipids, proteins, and DNA leads to severe inflammatory and degenerative pathologies seen in BD In this study, oxidant/antioxidant status of patients with BD was evaluated in comparison with controls and in respect to disease activity by measuring serum nitrite/nitrate, vitamin A, malondialdehyde (MDA), 8-hydroxy deoxyguanosine (8-OHdG), and total sulfhydryl levels (T-SH). The increase in serum MDA and 8-OHdG levels (respectively 30.04 vs. 17.93 nmol/ml, P = 0.0004 and 1.60 vs. 1.03 ng/ml, P = 0.0019) and the decrease in T-SH levels of patients with BD in comparison with controls (0.69 vs. 0.76 mmol/l, P = 0.0085) all indicate the impaired oxidant/antioxidant status in BD. The positive correlation found between MDA/8-OHdG levels (P = 0.02), and the negative correlations both between T-SH/8-OHdG levels (P = 0.031) and T-SH/MDA levels (P = 0.009) show the concordance between the parameters evaluating oxidant-antioxidant status. Among the parameters used for evaluating oxidant/antioxidant status, serum 8-OHdG was the only one showing significantly higher levels in patients with clinically active disease in comparison (P = 0.004) to patients in inactive period. Therefore, 8-OHdG that is assessed for the fist time in BD with this study can be proposed as a more reliable indicator of oxidant stress in evaluating disease activity.