AIM: The aim of our study was to determine the prevalence of anti-C1q antibodies and their possible association with clinical presentation in Behcet's disease (BD) patients with special emphasis for patients with vascular involvement. METHODS: Plasma anti-C1q Abs levels were measured using an enzyme-linked immunosorbent assay in 51 BD patients and 25 age- and gender-matched healthy controls. RESULTS: We found elevated concentrations of anti-C1q more frequently in patients with BD (18 %) than in healthy controls (8 %). The highest prevalence was found in patients with vascular BD (42 %) which was significantly higher than patients without vascular BD and healthy controls (p = 0.025). Furthermore, patients with vascular BD had the highest mean anti-C1q levels when compared to BD patients without vascular involvement or healthy control subjects (p = 0.015). We did not find significant differences in the prevalence of any other organ involvement between BD patients with elevated vs. normal anti-C1q ab levels. Anti-C1q ab levels positively correlated with ESR (r = 0.383, p = 0.006) and negatively with C4 (r = -0.304, p = 0.030). CONCLUSION: In conclusion, we found an increased prevalence of anti-C1q autoantibodies in BD patients with vascular involvement. Further large scale longitudinal studies are required to assess and clarify the significance and the pathogenic role of anti-C1q antibodies in BD and other autoimmune diseases in which vasculitis is a component.