Resistance to activated protein C (APCR), shown to be the most common genetic risk factor for venous thrombosis, is mostly caused by a mutation in the factor V (FV) gene leading to FV Leiden. As dural arteriovenous fistulas (DAVFs) are associated with cerebral venous thrombosis, we looked for the FV Leiden mutation in seven patients with such fistulas. The APCR ratio was determined according to standard procedures. For APCR ratios considered pathological (less than 2.0), mutation analysis was done by a reverse hybridization assay. Three of the seven patients with DAVFs showed pathological APCR ratios and heterozygosity for FV Leiden mutation. Thus, it is hypothesized that FV Leiden might be involved in the pathogenesis of DAVFs.