PURPOSE: To compare the incidence of surgical site occurrences (SSOs) following onlay versus preperitoneal mesh placement in elective open umbilical hernia repairs.METHODS: This study presents a secondary analysis of a randomized double-blind trial conducted on female patients with primary umbilical hernias admitted to a general hospital, in a residency training program setting. Fifty-six subjects were randomly assigned to either onlay (n=30) or preperitoneal (n=26) mesh repair group. Data on baseline demographics, past medical history, perioperative details, postoperative pain (visual analogue scale, VAS), wound-related complications and recurrence were assessed using a standardized protocol.RESULTS: No statistically signi cant differences were observed between groups regarding patients' demographics, comorbidities or defect size. Operative time averaged 67.5 (28 -110) minutes for onlay and 50.5 (31 -90) minutes for preperitoneal repairs, p=.03. The overall rate of SSOs was 21.4% (n=12), mainly in the onlay group (33% vs 7.7%; p=0.02, 95% CI 0.03 -0.85) and mostly due to seromas. There were no between-group signi cant differences in postoperative VAS scores at all timepoints. After a maximum follow-up of 48 months, one recurrence was reported in the onlay group. By logistic regression, the onlay technique was the only independent risk factor for SSOs.CONCLUSION: The presented data identi ed a decreased wound morbidity in preperitoneal umbilical hernia repairs, thus providing a good level of evidence for recommendations regarding mesh place selection in future guidelines. Further cases from this ongoing study and completion of follow-up are expected to also compare both techniques in terms of long-term outcomes.