Pregnancy may increase the risk of stroke. However, few studies have compared strokes in women of reproductive age that occur in pregnancy or the puerperium (pregnancy-related stroke, PRS) with those unrelated to pregnancy. This study assesses risk factors and etiologies of stroke in these women based on relationship to pregnancy. From 1984 to 2002, all female patients 15 through 40 years of age with a first-ever stroke at National Taiwan University Hospital were included in this study. PRS was defined as patients who had stroke occurrence during pregnancy or within 6 weeks postpartum. Stroke was categorized as cerebral infarction (CI), cerebral hemorrhage (CH), or subarachnoid hemorrhage (SAH) and divided into subtype according to etiology. Risk factors and etiologies were compared for patients with PRS and stroke unrelated to pregnancy. We identified 49 patients with PRS, and 353 patients with stroke unrelated to pregnancy. There was no statistically significant difference in distribution of CI subtypes. Cerebral venous thrombosis (CVT) was more common in PRS than stroke unrelated to pregnancy (39% vs. 7%, P<0.001), and 73% of these cases occurred postpartum. Preeclampsia-eclampsia was an important cause of peripartum CH (37%), but not CI (4%). Among PRS cases, postpartum cerebral venous thrombosis and preeclampsia-eclampsia were the major causes of CI and CH, respectively.