Objective To investigate whether women with epilepsy have an increased risk of complications during pregnancy and to explore the impact of antiepileptic drug (AED) use. Design Population-based cohort study. Setting Data from Medical Birth Registry of Norway based on all births in Norway 1999-2005. Population All births (n = 372 128) delivered in Norway, ensured through linkage with the National Population Registry run by Statistics Norway. All singleton births and the first child in multiple pregnancies were included, leaving 365 107 pregnancies for analyses. Main outcome measures Pre-eclampsia (mild and severe), gestational hypertension, eclampsia, vaginal bleeding (early and late) and preterm birth. Results We compared 2805 pregnancies in women with a current or past history of epilepsy (0.8%) and 362 302 pregnancies in women without a history of epilepsy. Women with epilepsy had an increased risk of mild pre-eclampsia, [odds ratio 1.3: 95% confidence interval (1.1-1.5)] and delivery before week 34 [1.2: (1.0-1.5)]. Antiepileptic drugs were used in 33.6% (n = 942) of the pregnant women with epilepsy. Compared to women without epilepsy, women with epilepsy and AED use had an increased risk of mild pre-eclampsia [1.8: (1.3-2.4)], gestational hypertension [1.5: (1.0-2.2)], vaginal bleeding late in pregnancy [1.9: (1.1-3.2)], and delivery before 34 weeks of gestation [1.5: (1.1-2.0)]. No significant increase in the risk of these complications was observed in women with epilepsy not using AED. These results remained unchanged after exclusion of multiple pregnancies. Conclusion Women with epilepsy have a low complication rate, but special attention should be paid to those using AED during pregnancy.