Purpose: A recent meta-analysis showed that the prevalence of irritable bowel syndrome (IBS) in South America (including Peru) is 21%, much higher than the worldwide global prevalence of 11.2% (95% CI 9.8%-12.8%). The aim of this study was to assess the role of intestinal parasites as a contributing factor to the high prevalence of IBS in Peru. Methods: We performed a population-based case-control study in Peruvian adults enrolled in military. IBS cases were identified using Rome III diagnostic criteria. All participants with no IBS criteria were selected as controls. One stool specimen was examined in all participants by directed microscopy, spontaneous sedimentation technique for detection of cysts and eggs, Baermann's technique for detection of larvae of Strongyloides and culture for Blastocystis spp. Mantel-Hanszel odd ratios were calculated to determine the association between IBS and intestinal parasites. Results: A total of 195 subjects (29.7% female) with a median age of 20 years (range: 17-38 years were included in the study. The overall prevalence of IBS was 20% (n=39), and when subjects with pathogenic parasites were excluded was 22% (n=23; p=0.7). Intestinal pathogenic parasites were detected in 16 (41%) patients with IBS and 75 (48%) in the control group (p=0.4). There was no statistically significant difference between the control group and IBS patients in terms of biparasitism (p=0.7) or multiparasitism (p=0.6). The common commensal parasite Blastocystis spp was present in 48.7% of the cases and 71.8% of the controls (OR 0.37; 95% CI 0.17-0.81; p<0.01). Presence of Ascaris lumbricoides, Trichuris trichiura, hookworm, Strongyloides stercoralis, Giardia lamblia, and Hymenolepis nana were not significantly associated in patients with IBS (Table 1).Table 1: Parasite carriage among IBS cases and healthy controlsConclusion: High prevalence of IBS in Peru was not associated with the presence of pathogenic intestinal parasites. In contrast to previous data, we found a negative association between Blastocystis spp. (commensal parasite) and IBS. Further population-based epidemiologic studies are warranted to determine specific risk factors that may contribute to high prevalence of IBS in South America.