Objectives: Basic and clinical studies had revealed a strong correlation between matrix metalloproteinases (MMPs), particularly MMP-9, and the formation of abdominal aortic aneurysms. In addition, previous studies had clearly shown that MMP-9 plays an important role in the pathogenesis of vasculitis characterized by aneurysm formation such as Kawasaki disease, temporal arteritis and Takayasu arteritis. Depending on those findings, we hypothesized that circulating MMP-9 could be useful marker to demonstrate vascular involvement in patients with BD.Methods: Thirty patients with BD, and 20 healthy controls were enrolled in the study. We assessed the disease activity of patients according to the Leeds activity score system (BDCAF). We compared the Leeds activity scores of patients with their serum levels of MMP- 9. Patients with BD were categorized as active (total activity score ≥ 5) or inactive (total activity score < 5). Patients were further categorized with respect to their extent of involvement as those with and those without vascular involvement. The level of MMP-9 was measured by ELISA.Results: Serum MMP-9 level was significantly higher both in patients with active and inactive disease as compared to healthy controls (p < 0.001). We found positive correlation between serum level of MMP-9 and disease activity assessed by BDCAF particularly the vascular affection whether on the venous or the arterial side. Conclusions: We concluded that serum MMP-9 levels can be used in the diagnosis and assessment of disease activity in general and vascular activity in particular in BD.