ORIGINAL ARTICLE Reproductive epidemiology The co-occurrence of endometriosis with multiple sclerosis, systemic lupus erythematosus and Sjogren syndrome

background: In a previous study, women with endometriosis were found to be at a 7–24-fold increased risk of multiple sclerosis (MS), systemic lupus erythematosus (SLE) and Sjögren syndrome (SS). We examined these associations in a large population-based cohort study. methods: We followed 37 661 women registered with endometriosis in the Danish Hospital Discharge Register 1977–2007 for sub-sequent hospitalizations with MS, SLE or SS. As measures of relative risk, we used ratios of observed to expected incidence rates of first hospitalizations for MS, SLE and SS among women with endometriosis, i.e. standardized incidence ratios (SIR) with accompanying 95 % con-fidence intervals (CIs).