INTRODUCTION: Vitamin D (vitD) is a substance with an immunomodulatory effect. Its insufficiency has negative impact also on inflammatory bowel disease (IBD) where it is often present. The recommended daily intake for general population is 600 UI/day (units/day). What is the necessary dose for IBD patients remains unknown. The aim of the study was to verify whether the 2,000 IU/day of vitD is sufficient for maintaining sustained levels in these patients. METHODS: Patients with Crohns disease (CD) or ulcerative colitis (UC) were supplemented orally with 2,000 IU of cholecalciferol daily during winter time. The level of 25-hydroxyvitamin D (25OHD) was established at the beginning of substitution period (October to December) and in Month 4. Demographic data, Ca, P, parathormone levels, dose of vitD used, and patients compliance were observed. RESULTS: 108 patients with CD and UC (71/37) were analysed, out of them 51 females, average age 43.3 ± 16.2 years. The level of 25OHD increased from 60.2 ± 26.5 nmol/l to 68.1 ± 27.1 nmol/l (p < 0.001) during the period with the average substitution dose of vitD 1 858 ± 464 IU/day. 60.2 % of subjects complied with the recommended dosing of vitD. The dose of 1,820 IU vitD/day showed to be sufficient for maintaining sustained levels in the model. No changes of Ca, P serum levels occurred during observation period. CONCLUSIONS: Substitution doses of vitD recommended for general population are insufficient for IBD patients. A dose of up to 2,000/day, which is safe, is necessary to maintain normal levels of 25OHD. Noncompliance with the use of vitD is high.