David Bergman,1 Bjorn Roelstraete,1 Jiangwei Sun,1 Fahim Ebrahimi,1,2 Rickard Lidström,3 Axel Svedbom,4,5 Mona Ståhle,4 Jonas F Ludvigsson1,6,7 1Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; 2Department of Gastroenterology and Hepatology, Clarunis University Center for Gastrointestinal and Liver Diseases, Basel, Switzerland; 3Diagnostiskt Centrum Hud, Stockholm, Sweden; 4Division of Dermatology and Venereology, Department of Medicine, Karolinska Institutet, Stockholm, Sweden; 5Dermatology and Venereology Clinic, Karolinska University Hospital, Stockholm, Sweden; 6Department of Pediatrics, Orebro University Hospital, Orebro, Sweden; 7Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY, USACorrespondence: David Bergman, Email [email protected]: Microscopic colitis (MC) has been associated with several immune-mediated diseases including psoriasis, but earlier research has been limited to psoriasis occurring before MC. Data from large-scale cohort studies investigating MC and risk of future psoriasis are lacking.Objective: To examine the association between MC and psoriasis.Methods: In a nationwide, population-based, matched cohort study in Sweden from 2007 to 2021, we identified 8404 patients with biopsy-verified MC (diagnosed in 2007– 2017), 37,033 matched reference individuals, and 8381 siblings without MC. Information on MC was obtained through the ESPRESSO cohort (a Swedish histopathology database with nationwide coverage). Using Cox regression, we calculated hazard ratios (HRs) and 95% confidence intervals (CIs) for psoriasis up until 2021.Results: During a median follow-up of 9.2 years (interquartile range = 6.7– 11.7), 179 MC patients and 440 reference individuals were diagnosed with psoriasis (241.1 vs 131.8 events per 100,000 person-years), corresponding to one extra case of psoriasis in 91 patients with MC over 10 years. After adjustment for the matching variables (birth year, sex, county of residence, and calendar period) and level of education, we computed an adjusted hazard ratio (aHR) of 1.82 (95% CI = 1.53– 2.17). Stratified by sex, estimates were similar and when examining the aHR across different lengths of follow-up, we found significantly elevated estimates up to 10 years after MC diagnosis. Compared to MC-free siblings, the aHR was 1.85 (95% CI = 1.36– 2.51).Conclusion: Patients with MC are at an almost doubled risk of psoriasis compared to the general population. Clinicians need to consider psoriasis in MC patients with skin lesions.Keywords: microscopic colitis, psoriasis, epidemiolog