Abstract Background and aims. Collagenous colitis (CC) is associated with autoimmune disorders. The aim of the present study was to investigate the relationship between CC and autoimmune disorders in a Swedish multicenter study. Methods. Patients with CC answered questionnaires about demographic data and disease activity. The patient's files were scrutinized for information about autoimmune diseases. Results. A total number of 116 CC patients were included; 92 women, 24 men, median age 62 years (IQR 55-73). In total, 30.2% had one or more autoimmune disorder. Most common were celiac disease (CeD; 12.9%) and autoimmune thyroid disease (ATD, 10.3%), but they also had Sjögren's syndrome (3.4%), diabetes mellitus (1.7%) and conditions in skin and joints (6.0%). Patients with associated autoimmune disease had more often nocturnal stools. The majority of the patients with associated CeD or ATD got these diagnoses before the colitis diagnosis. Conclusion. Autoimmune disorders occurred in one-third of these patients, especially CeD. In classic inflammatory bowel disease (IBD), liver disease is described in contrast to CC where no cases occurred. Instead, CeD was prevalent, a condition not reported in classic IBD. Patients with an associated autoimmune disease had more symptoms. Patients with CC and CeD had an earlier onset of their colitis. The majority of the patients with both CC and CeD were smokers. Associated autoimmune disease should be contemplated in the follow-up of these patients.