Purpose <p>The actual incidence of incisional hernia (IH) after abdominal aortic aneurysm repair in Japanese patients is unknown. This study examined the incidence of IH after aortic reconstruction surgery.</p> Methods <p>Patients who underwent elective midline laparotomy for AAA at a single institution between November 2012 and September 2021 were retrospectively analyzed. The primary endpoint was IH diagnosed by physical examination and CT.</p> Results <p>A total of 285 patients were analyzed. The median follow-up was 3.7&#xa0;years (interquartile range: 1.6–5.9&#xa0;years). 67 patients (23.5%) developed IH; of these patients, 16 (23.9%) underwent hernia repair. The cumulative incidence of IH was 28.0% at five years. According to a multivariate analysis, body mass index (BMI) was identified as an independent risk factor for IH (hazard ratio, 1.22; 95% confidence interval: 1.13–1.32, <i>p</i> &lt; 0.001). Obese patients with BMI ≥ 25&#xa0;kg/m² had a significantly higher incidence of IH than normal-weight patients with BMI of 18.5 to 25&#xa0;kg/m² (5-year cumulative incidence: 44.5% vs. 22.1%, <i>p</i> = 0.001), and underweight patients with BMI &lt; 18.5&#xa0;kg/m² had no IH.</p> Conclusion <p>Approximately half of all obese patients developed IH within 5&#xa0;years, although underweight patients had no IH.</p>