BACKGROUND & AIMS: Irritable bowel syndrome (IBS) is the most commonly diagnosed gastrointestinal condition and is most prevalent in women of reproductive age. We investigated the effects of IBS on risk for adverse outcomes from pregnancy. METHODS: We conducted a cohort study by using the United Kingdom General Practice Research Database. The study cohort consisted of 100,000 women selected by stratified random sampling from all women with a diagnosis of pregnancy from January 1, 1990, to December 31, 2008. Those with a recorded diagnosis of IBS before pregnancy were identified (n = 26,543). Outcome measures were spontaneous miscarriage, ectopic pregnancy, preeclampsia, and stillbirth. Odds ratios (ORs) and 95% confidence intervals (CIs) for the association between IBS and pregnancy outcomes were estimated by using logistic regression adjusted for several potential confounders. RESULTS: Of women diagnosed with IBS before pregnancy, 6578 (7%) had a spontaneous miscarriage, 741 (0.74%) had an ectopic pregnancy, 425 (0.43%) developed preeclampsia, and 217 (0.22%) had a stillbirth. Maternal IBS was associated with a moderately increased risk of miscarriage (OR, 1.21; 95% CI, 1.13-1.30) and ectopic pregnancy (OR, 1.28%; 95% CI, 1.06 - 1.55). There did not appear to be an association between IBS and preeclampsia (OR, 1.09; 95% CI, 0.85-1.39) or stillbirth (OR, 1.00; 95% CI, 0.69 - 1.44). CONCLUSIONS: IBS, a common disorder in women of reproductive age, appears to increase the risk of miscarriage and ectopic pregnancy. These findings indicate the importance of prenatal care for women with IBS.