Introduction: there are few data on the prevalence of vitamin D deficiency in patients with inflammatory bowel disease (IBD) in Spain. A deficiency could be associated with a worse course of the disease. Aim: to determine the prevalence of 25-hydroxyvitamin D (25OHD) deficiency in a cohort of outpatients with IBD and assess its association with clinical and biological activity, quality of life and psychological symptoms. Methods: a cross-sectional, single-center observational study was performed. The study variables were obtained via clinical interviews, medical chart review and validated questionnaires (Hospital Anxiety and Depression Scale and Short Quality of Life in Inflammatory Bowel Disease Questionnaire). 25OHD was measured in the same laboratory by an electro-chemiluminescence immunoassay. Results: the study included 224 patients. The prevalence of vitamin D deficiency in Crohn's disease and ulcerative colitis was 33.3% and 20.3%, respectively. In Crohn's disease, vitamin D deficiency was associated with a higher clinical activity (p < 0.001) and a higher concentration of fecal calprotectin (p = 0.01). In ulcerative colitis, it was associated with clinical activity (p < 0.001), the use of steroids during the last six months (p = 0.001) and hospital admission during the previous year (p = 0.003). A subanalysis of 149 patients failed to detect an association between vitamin D and quality of life or the scores of the Hospital Anxiety and Depression Scale. Conclusions: vitamin D deficiency is common in patients with inflammatory bowel disease. An association was found between vitamin D concentration and clinical activity indexes, as well as fecal calprotectin levels in Crohn's disease.