Reintervention rates after patch-augmented reconstruction for hypoplastic aortic arch remain moderately high. We analyzed mid-term outcomes of aortic arch reconstruction to define modifiable reintervention risk factors. Excluding Damus-Kaye-Stansel anastomoses and previous arch repair, 338 patients underwent arch reconstruction from 2000-2021 at median age 6d (IQR 4-13d) and weight 3.2kg (IQR 2.8-3.7kg). Surgical technique was patch augmentation with coarctectomy ± interdigitation in 269 (80%), isolated patch aortoplasty in 41 (12%), and other reconstruction in 28 (8%). Risk factors for reintervention were assessed using competing risk models. At median follow-up of 3.9y (IQR 1.1-8.0y), 35 (10.4%) patients required reintervention (30 endovascular, 12 surgical, 7 both). Ten-year cumulative incidence of death/transplant and reintervention were 10% (95%CI 4-20%) and 13% (95%CI 8-20%). On univariate analysis, isolated patch aortoplasty (p=0.002), aortic homograft patch material (p=0.006), and postoperative aortic size z-score ≤-2 for each segment were associated with greater risk of reintervention: ascending aorta (p=0.006), proximal (p=0.001) and distal (p=0.005) transverse arch, and aortic isthmus (p<0.001). On multivariable analysis, aortic homograft (HR 6.29, 95%CI 1.94-20.5, p=0.002) and postoperative isthmus z-score ≤-2 (HR 10.5, 95%CI 5.15-21.5, p<0.001) remained significant. Patients with repaired isthmus z-score ≤-2 had 72.8% (95%CI 44.6-94.4%) cumulative incidence of reintervention at 10 years, versus 6.8% (95%CI 4.1-11.4%) in those with z-score >-2. Aortic undersizing during patch-augmented reconstruction of hypoplastic aortic arch results in over 10% rate of reintervention at mid-term follow-up. Achieving adequate postoperative arch size is critical for preventing reintervention, with aortic isthmus size being of utmost importance.