Acquired and hereditary thrombophilias are associated with obstetric complications such as (pre-)eclampsia, HELLP syndrome and fetal loss. Our objective was to assess the risk of obstetric complications in women with elevated levels of FVIII:C or hyperhomocysteinemia, as compared with their relatives who had normal FVIII:C or homocysteine levels. From a large family study of patients with venous thromboembolism or premature atherosclerosis and elevated levels of FVIII:C or hyperhomocysteinemia (propositi), the obstetric histories of female first degree relatives, who had been pregnant at least once, were studied. Levels of FVIII:C and homocysteine (both fasting and post-methionine loading) were determined. The number of obstetric complications was calculated and compared in women with normal and elevated levels of FVIII:C, and normal and elevated levels of homocysteine. Women with elevated levels of FVIII:C had a 15.4% risk for toxicosis, preeclampsia, or HELLP syndrome and a 23.9% for fetal loss. This was not statistically different from women with normal levels of FVIII:C. Women with hyperhomocysteinemia tended to have a lower risk for toxicosis, pre-eclampsia, or HELLP syndrome (8.0%, RR 0.6, 95% CI 0.2-1.7) and fetal loss (22.0%, RR 0.8, 95% CI 0.5-1.5) as compared to relatives with normal levels, although these differences did not reach statistical significance. If the analysis was limited to comparing extremes, the results did not materially differ. Unselected women with elevated plasma levels of FVIII:C or hyperhomocysteinemia are not at increased risk for obstetric complications as compared to their relatives with normal levels.