Objective: To determine a family aggregation pattern of Irritable Bowel Syndrome (IBS). Design: it is a case-control study with a 1.2 ratio. Setting. External consultation of a general family medicine practice.Participants: men and women from 18 to 60 years old. Cases (40): people with IBS according to the Rome IV criteria, and Controls (80): relatives without gastrointestinal disease. Main measurements. Sociodemographic variables, related stressful events, predominant evacuation patterns, and family repetition patterns for IBS. Data were analyzed with descriptive and inferential statistics. Chi-square for categorical data (< p.05 as significant) estimate of ORs with 95% confidence interval. The institutional ethics committee approved it. Results: The IBS presentation pattern was repeated in relatives, mainly first-degree. The risk of suffering from IBS was higher when the father reported it (OR 11.2 (95% CI; 1.2-100.1), than the mother OR 3,7 (95% CI; 1.4 --9.9), sibling OR 2.8 (95% CI; 1.1 --6.6. In both groups, the relative who most frequently presented IBS was in the collateral line (sibling) (37.5% in cases vs. 17.5% in controls (p = 0.023). In both groups, the predominant gender was female, with 80. 0% in cases and 57.5% in controls.Conclusion: SII has a familial recurrence pattern in the Mexican population. The disease is more frequent in first-degree relatives. It is important to elucidate the importance of the role that plays genetic background vs. the influence of the family environment in SII.(c) 2023 The Authors. Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY-NC-ND license.