Vitamins are micronutrient chemical compounds that cannot be synthesized by an organism but are essential for human metabolism and life. They act as required intermediaries, cofactors or coenzymes in many of the reactions of normal metabolism. In addition, anti-inflammatory effects have been reported for specific vitamins. In inflammatory bowel disease (IBD), vitamin deficiency is often due to malnutrition (due to a decreased food intake) or malabsorption (due to inflamed, malfunctioning mucosa and diarrhea) which results in anemia. Vitamin B-12 and folic acid supplementation may be necessary in IBD patients, especially those with Crohn's disease (CD) with either inflammation of the terminal ileum or after resection of the terminal ileum. It is also recommended during therapy with sulfasalazine as this compound inhibits the absorption of vitamin B-12. Patients with high or continuous inflammatory CD activity and frequent therapy with steroids have an increased risk of low bone mineral density and vitamin D deficiency. These should be monitored regularly and vitamin D should be supplemented. In a recent trial, a trend towards a reduced risk of relapses in CD patients treated with vitamin D was reported. Only limited studies and case reports exist on other vitamin deficiencies, e.g. vitamins A, B-1, B-2, niacine, B-6, C, E and K, found in IBD patients. These are summarized in this review. Regular nutritional monitoring in IBD patients is warranted and requires the special attention of treating physicians and dieticians. Copyright (C) 2012 S. Karger AG, Basel