Venous thrombosis (VT) is a common disease, with an annual incidence in the general population of approximately 1 per 1,000. Factor V Leiden mutation (G1691A) (FVL) is the most common risk factor in venous thrombosis. The prevalence of FVL for thrombosis varies greatly in different regions of the world. FVL mutation has been identified both by conventional method and fluorescence resonance energy transfer (FRET) with the LightCycler. Sixty-one patients with VT, different in age and sex, were consecutively entered into this study to assess the prevalence of FVL in VT in southeast Turkey. FVL mutation was found in 24.6% (15/61). Fourteen individuals were heterozygous and 1 homozygous, a rate of 22.9% and 1.6%, respectively. In conclusion, the authors suggest that FVL mutation is common in patients with venous thrombosis in southeast Turkey.