Background: Vitamin D deficiency is common in inflammatory bowel disease (IBD). The aim of the study was to determine the prevalence and predictors of vitamin D deficiency in an IBD cohort. It was hypothesized that vitamin D deficiency is associated with increased disease activity and lower health‐related quality of life (HRQOL). Methods: This was a retrospective cohort study. Harvey‐Bradshaw index and ulcerative colitis disease activity index were used to assess disease activity. Short Inflammatory Bowel Disease Questionnaire scores were used to assess HRQOL. Multivariate logistic regression was used to identify independent predictors of vitamin D deficiency and its association with disease activity and HRQOL. Results: The study included 504 IBD patients (403 Crohn's disease [CD] and 101 ulcerative colitis [UC]) who had a mean disease duration of 15.5 years in CD patients and 10.9 years in UC patients; 49.8% were vitamin D deficient, with 10.9% having severe deficiency. Vitamin D deficiency was associated with older age (P = .004) and older age at diagnosis (P = .03). Vitamin D deficiency was associated with lower HRQOL (regression coefficient –2.21, 95% confidence interval [CI], –4.10 to –0.33) in CD but not UC (regression coefficient 0.41, 95% CI, –2.91 to 3.73). Vitamin D deficiency was also associated with increased disease activity in CD (regression coefficient 1.07, 95% CI, 0.43 to 1.71). Conclusions: Vitamin D deficiency is common in IBD and is independently associated with lower HRQOL and greater disease activity in CD. There is a need for prospective studies to assess this correlation and examine the impact of vitamin D supplementation on disease course.