BackgroundEndometriosis and irritable bowel syndrome (IBS) have similar symptoms, pathogenesis, and risk factors. These diagnoses often coexist and are frequently misdiagnosed leading to diagnostic delays. This study of a population-based cohort aimed to investigate associations relating to endometriosis and IBS and to compare gastrointestinal symptoms between endometriosis and IBS.MethodThe study cohort included women from the Malmö Offspring Study with information about endometriosis and IBS diagnoses from the National Board of Health and Welfare. The participants answered a questionnaire about lifestyle habits, medical and drug history, and self-reported IBS. The visual analog scale for IBS was used to estimate gastrointestinal symptoms the past 2 weeks. Endometriosis diagnosis and self-reported IBS were used as dependent variables to study associations with age, body mass index (BMI), education, occupation, marital status, smoking, alcohol habits, and physical activity using logistic regression. Mann-Whitney U Test or Kruskal-Wallis tests were used to calculate the differences in symptoms between groups.ResultsOf the 2,200 women with information from medical records, 72 participants had endometriosis; 21 (29.2%) of these had self-reported IBS. Of the 1,915 participants who had answered the questionnaire, 436 (22.8%) had self-reported IBS. Endometriosis was associated with IBS (OR:1.86; 95%CI:1.06–3.26; p = 0.029), as well as with age 50–59 years (OR:6.92; 95%CI:1.97–24.32; p = 0.003), age ≥ 60 years (OR:6.27; 95%CI:1.56–25.17; p = 0.010), sick leave (OR:2.43; 95%CI:1.08–5.48; p = 0.033), and former smoking (OR:3.02; 95%CI:1.19–7.68; p = 0.020). There was an inverse association with BMI (OR:0.36; 95%CI:0.14–4.91; p = 0.031). IBS was associated with endometriosis (OR:1.77; 95%CI:1.02–3.07; p = 0.041) and sick leave (OR:1.77; 95%CI:1.14–2.73; p = 0.010), with a tendency to association with smoking (OR:1.30; 95%CI:0.98–1.72; p = 0.071). When excluding participants using drugs associated with IBS, the condition was associated with current smoking (OR:1.39; 95%CI:1.03–1.89; p = 0.033) and inversely with age 50–59 years (OR:0.58; 95%CI:0.38–0.90; p = 0.015). There were differences in the gastrointestinal symptoms between IBS and healthy participants, but not between endometriosis and IBS or healthy participants.ConclusionThere were associations between endometriosis and IBS, without differences in gastrointestinal symptoms. Both IBS and endometriosis were associated with smoking and sick leave. Whether the associations reflect causality or depend on common risk factors and pathogenesis remains to be determined.