ObjectivesAdverse childhood experiences (ACE) are associated with immune-mediated inflammatory diseases (IMID). We evaluated whether: (i) ACE associate with psychiatric comorbidity among individuals with IMID, including rheumatoid arthritis (RA), multiple sclerosis (MS), and inflammatory bowel disease (IBD); (ii) whether psychiatric disorders mediate the relationship between ACE and IMID; and (iii) whether these findings differ from those in individuals with other chronic physical disorders. MethodsUsing data from the Canadian Longitudinal Study on Aging (CLSA) we performed a retrospective case-control study of participants aged 45–85 years recruited between 2010 and 2015. ACE were queried using questions derived from the Childhood Experiences of Violence Questionnaire-Short Form and the National Longitudinal Study of Adolescent to Adult Health Wave III questionnaire. We used multivariable logistic regression and causal mediation analysis to address our objectives. ResultsWe included 13,977 CLSA participants. Among the 31 % of IMID participants who reported a comorbid psychiatric disorder, 79 % reported a history of ACE. ACE associated with increased odds (OR [95 % CI]) of a psychiatric disorder (2.55 [1.02–6.35]) among participants with IMID; this did not differ across IMID. The total effect (OR [95 % CI]) of ACE on IMID was 1.11 (1.07–1.16), of which 10.60 % (8.04–17.47) was mediated by psychiatric disorders. We found similar associations among participants with other chronic physical disorders. ConclusionOur findings suggest that psychiatric disorders partially mediate the association between ACE and IMID. Most participants with IMID and comorbid psychiatric disorders report a history of ACE and may benefit from trauma-informed mental health care.