Background: Vitamin D is a steroid hormone that is produced as a result of skin exposure to the sunlight. Vitamin D is essential to different organs and systems in the body as the bones, intestines, immune system, pancreas, brain, and control of cell cycle. Aim of the work: to assess the clinical relevance of vitamin D in colonic diseases (IBS and IBD) to know if there is a prevalence of vitamin D deficiency in these colonic diseases.Patients and Methods: This study was performed on 90 Egyptian patients who were classified into 3 groups; where Group 1 included 30 patients who have irritable bowel syndrome (IBS), Group 2 30 patients who have inflammatory bowel disease (IBD) whether Ulcerative Colitis (UC) or Crohn's Disease (CD) and Group 3 30 healthy personnel taken as Control group.Results: Regarding different vitamin D levels in the studied groups. In the control group, (20%) had deficient vitamin D level (< 20 ng/ml), (30%) had insufficient vitamin D level (20 -30 ng/ml), (50%) had optimal vitamin D level (>30 ng/ml). In IBS group, (60%) had deficient vitamin D level, (26.7%) had insufficient vitamin D level, (13.3%) had optimal vitamin D level. In the UC group, (66.7%) had deficient vitamin D level, (16.7%) had insufficient vitamin D level, (16.7%) had optimal vitamin D level. In CD group, (50%) had deficient vitamin D level, (33.3%) had insufficient vitamin D level, (16.7%) had optimal vitamin D level. Conclusion:The role of vitamin D deficiency in the pathogenesis of many chronic illnesses has raised the attention recently. Our study revealed that 25-OH-D3 deficiency is found more frequently among UC, CD and IBS patients than normal healthy controls. Thus, vitamin D prescription in these patients may help in improving these colonic diseases.