We conducted a retrospective analysis of 451 women with an arteriovenous malformation (AVM) of the brain to determine whether pregnancy is a risk factor for cerebral hemorrhages. A total of 540 pregnancies occurred among our patient population, resulting in 438 live births and 102 abortions. There were 17 pregnancies complicated by a cerebral hemorrhage. The hemorrhage rate during pregnancy for women with an unruptured AVM was 0.035 +/- 0.005 per person-year. The hemorrhage rate for nonpregnant women of childbearing age with an unruptured AVM was 0.031 +/- 0.002 per person-year. Pregnancy did not increase significantly the rate of first cerebral hemorrhage from an AVM (P = 0.35). We found that women with an AVM face a 3.5% risk of hemorrhage during pregnancy. Pregnancy is not a risk factor for hemorrhage in women without a previous hemorrhage. This conclusion assumes no selection bias exists in our study population; a bias would be introduced if the risk of fatal outcome after a hemorrhage were greater in pregnant women than in nonpregnant women.