Objectives: Vitamin D has been found to be strongly associated with many systemic disorders. There has been an augmented interest within the medical community in vitamin D, especially its deficiency, in various systemic disorders. Although the role of vitamin D deficiency in irritable bowel syndrome (IBS) has not yet been established, studies are underway to clearly establish its role in the disease. The objective of the our study was to elucidate and establish the role of vitamin D deficiency in IBS patients compared to a healthy control group. Methods: This study is a comparative case control study of vitamin D deficiency in patients with IBS diagnosed with ROME 3 criteria of classification (the third ROME foundation classification) to an age and gender matched healthy control group. The vitamin D level was measured in both cohorts for comparison and the results interpreted statistically. Sixty patients with IBS and 100 healthy individuals were included as test and control groups, respectively, in the study. The mean serum vitamin D level (nmol/L) of IBS patients was compared to the control group. Results: Vitamin D deficiency was detected in 49 patients (82%) in the IBS group and 31 patients (31%) in the control group. There was a statistically significant difference in the mean vitamin D level (p=0.025) between the IBS group and control group. Conclusions: Our study shows that vitamin D deficiency is highly prevalent in patients with IBS and these results seem to have therapeutic implications. Vitamin D supplementation could play a therapeutic role in the control of IBS.