OBJECTIVE Anticardiolipin antibodies (aCL) have been recognized as a marker for an increased risk of thrombosis. There are no documented reports from India on the prevalence of aCL in patients with cerebral venous thrombosis (CVT). Our study aimed at establishing the prevalence of these antibodies in patients with CVT and evaluating their clinical significance. METHODS Thirty-one patients with CVT diagnosed by angiography and/or cranial CT were investigated for the presence of aCL along with 31 age- and sex-matched normal controls. All subjects had no overt evidence of systemic lupus erythematosis or related autoimmune disorders. The titres of IgG and IgM type of aCL were estimated in the sera using a solid phase enzyme-linked immunosorbent assay. RESULTS Anticardiolipin antibodies were detected in 22.6% of CVT patients compared to 3.2% of normal controls (95% confidence interval (CI) 1.01 to 75.65). Five CVT patients had both IgG and IgM antibodies, and 2 had only IgG antibodies. The aCL positive group did not differ from the aCL-negative group with respect to the clinical characteristics and the demographic and risk factor profile. CONCLUSIONS The findings suggest that anticardiolipin antibodies are a risk marker for cerebral venous thrombosis. Further studies on a larger group of patients are needed to establish the role of aCL in the pathogenesis of CVT.