BACKGROUND AND AIMS: Previous studies provide evidence that some immune-mediated diseases occur at greater frequency among inflammatory bowel disease (IBD) patients than in the general population. The present study examined the co-occurrence of IBD with common immune-mediated disorders including asthma, psoriasis, type 1 diabetes, rheumatoid arthritis, multiple sclerosis, systemic lupus erythematosus, vitiligo, autoimmune thyroiditis (Grave’s and Hashimoto’s), and chronic glomerulonephritis. METHODS: We conducted a cross-sectional study among members of the Kaiser Permanente Medical Care Program for the period 1996-2005. A total of 12,601 patients with at least two IBD diagnoses in computerized visit data were ascertained. Four persons without IBD were matched to each IBD patient on age, gender, and length of enrollment. Information on co-occurring diseases was obtained from computerized visit data for 1996-2005. Conditional logistic regression was used to estimate the odds ratio and 95% confidence interval for the association of IBD with immune-mediated disorders after adjusting for smoking. RESULTS: Seventeen percent of the IBD patients and 10% of the persons without IBD had a diagnosis for at least one immune-mediated disease. IBD patients were more likely to have asthma (1.5, 95% CI 1.4-1.6), psoriasis (1.7, 95% CI 1.5-2.0), rheumatoid arthritis (1.9, 95% CI 1.5-2.3), and multiple sclerosis (2.3, 95% CI 1.6-3.3). CONCLUSIONS: Among the immune-mediated diseases we studied, most were more common in IBD patients than in persons without IBD, suggesting that IBD shares common etiologic factors with other immune-mediated diseases.