Summary. Hereditary risk determinants of venous thrombosis have been reported to be associated with severe preeclampsia. So far there are no data to support whether these risk determinants are related to the time of onset of severe preeclampsia. We used a case–control design, studying 97 women with severe preeclampsia in previous pregnancies and 277 normal women, to assess hereditary risk factors of venous thrombosis as risk determinants for severe preeclampsia. A case-only design comprising solely the 97 women with a history of preeclampsia was used to evaluate these risk factors as risk determinants for early onset of severe preeclampsia. Using the case–control design, there was no significant risk association of the hereditary risk factors with severe preeclampsia [factor V Leiden, odds ratio (OR) 0.9, 95% confidence interval (CI) 0.4, 2.2; prothrombin mutation, OR 1.9, 95% CI 0.5, 7.0; methylentetrahydrofolate reductase 677TT genotype, OR 0.8, 95% CI 0.4, 1.8; plasminogen activator inhibitor (PAI-1) 4G/4G genotype, OR 1.2, 95% CI 0.7, 2.1; PAI-1 5G/5G genotype, OR 1.0, 95% CI 0.5, 1.8]. However, the onset of severe preeclampsia was significantly earlier in women with the G20210A prothrombin gene mutation (24.5 weeks vs. 30.1 weeks, P = 0.046) and in women with the PAI-1 5G/5G genotype (25.7 weeks vs. 30.8 weeks, P = 0.024). Hereditary risk factors for venous thrombosis do not predispose for severe preeclampsia. However, women who are carriers of the G20210A prothrombin gene mutation and the PAI-1 5G/5G genotype are at risk for early onset of severe preeclampsia. It appears that these risk factors do not induce the pathomechanism but accelerate the course of preeclampsia.