En 1680-6433 2008-2177 Background: Role of genetic factors in etiology of preeclampsia is not confirmed yet. Objective: Gene defect frequency varies in different geographic areas as well as ethnic groups. In this study, the role of factor V Leiden mutation in the pathogenesis of preeclampsia syndrome among the pregnant population of northern shore of Persian Gulf in Iran, were considered. Materials and Methods: Between Jan. 2008 and Dec. 2009, in a nested case control study, pregnant women with preeclampsia (N=198) as cases and healthy (N=201) as controls were enrolled in the study. DNA were extracted from 10 CC peripheral blood and analyzed for presence of factor V Leiden mutation in these subjects. The maternal and neonatal outcomes of pregnancy according to the distribution of factor V Leiden were also compared among cases. Results: In total, 17(8.6%) of cases and 2(1%) of controls showed the factor V Leiden mutation. The incidence of factor V Leiden was typically higher in preeclamptic women than control group (OR: 9.34 %95 CI: 2.12-41.01). There was no difference in incidence rate of preterm delivery< 37 weeks (OR: 1.23 %95 CI: 0.38-4.02), very early preterm delivery<32 weeks (OR: 1.00 %95 CI: 0.12-8.46), intra uterine fetal growth restriction (IUGR) (OR: 1.32 %95 CI: 0.15-11.30 ),and the rate of cesarean section (OR: 0.88 %95 CI: 0.29-2.62 ) among cases based on the prevalence of factor V Leiden mutation. Conclusion: The pregnant women with factor V Leiden mutation are prone for preeclampsia syndrome during pregnancy, but this risk factor was not correlated to pregnancy complications in the studied women. Preeclampsia, Factor V Leiden mutation, Obstetric complication, Iran. 59 66 Samieh Karimi No Majid Yavarian No Azadeh Azinfar aazinfar@yahoo.com No Minoo Rajaei No Maryam Azizi Kootenaee No