OBJECTIVE. Little is known about predictors for adverse pregnancy outcomes among women with Crohn's disease (CD). In this population-based study, we examined pregnancy outcomes in CD stratified by medical treatment and smoking status while accounting for disease activity. METHODS. In two Danish regions with a population of 1.6 million, we identified 154 CD women who had given birth within a 6-year period. We combined questionnaire data, prescription data, data from medical records and population-based medical databases. We used logistic regression to estimate prevalence odds ratios (POR) for adverse pregnancy outcomes by different predictors. RESULTS. Among 105 (80%) respondents, 55 (52%) reported taking medication during pregnancy. The majority (95%) were in disease remission. The children's mean birth weight did not differ by maternal medical treatment. As expected, smoking was a predictor of low birth weight. Mean birth weight in children of smokers in medical treatment was significantly reduced by 274 g compared with children of non-smokers who received medical treatment. In children of women without medical treatment, this difference was 126 g between smokers and non-smokers. Women in medical treatment did not have an increased risk of preterm delivery (POR 0.71; 95% confidence interval (CI) 0.18-2.79), congenital malformations (POR 0.60; 0.10-3.76) or cesarean section (POR 1.40; 0.63-3.08). CONCLUSIon. In CD, smoking was negatively associated with child birth weight. This association was most pronounced among women who received medical treatment. Maternal medical treatment for CD did not seem to be a risk factor for adverse pregnancy outcomes.