Abstract:The objective of this case control study is to identify the relationship between intestinal parasitic infection and Irritable Bowel Syndrome (IBS) among Sudanese patients. Method: Two hundred patients diagnosed with irritable bowel syndrome (IBS) and were attended Health Facilities at Khartoum State were enrolled, together with 99 apparently healthy controls. Patients were classified into three groups (IBS-all types, IBS with diarrhea (IBS-D), and IBS with constipation (IBS-C)). Stool specimens were collected form study population and all were subjected to microscopic examination following wet saline preparation, formal-ether concentration technique, Z. N stain, and in vitro cultivation in Locke egg medium. Results: Intestinal parasites were detected in 32% (64/200) of IBS-all types; and in 16.2% (16/99) of control group (P. value 0.005). For patients, 20 (10%) were positive for the Entamoeba cyst, 3 (1.5%) Giardia lamblia cysts, and 41 (20.5%) were positive for Blastocystis hominis cyst. For control, Entamoeba species were detected in 10 (10.1%), G. lambelia one case (1.1%), and B. hominis in 5 (5.2%). Blastocystis hominis was significantly prevalent among IBS-all types than the control group (P. value 0.02). It is more frequent among patients with IBS-D than those with IBS-C (P. value 0.001). Conclusion: This study concluded that, there is a statistical association between presence of intestinal parasites and IBS on study population. Blastocystis hominis was found more frequently detected parasite, and it was found significantly associated with IBS-diarrhea.