Background: The ideal position of suture annuloplasty relative to the aortic annulus (internal or external) remains unclear. This study aimed to investigate the effectiveness of internal and external suture annuloplasty for isolated type 1 bicuspid aortic valve (BAV) repair. Electrocardiogram (ECG)-gated computed tomography (CT) was used to compare the two techniques and analyze their impact on the aortic annulus. Methods: We retrospectively analyzed 20 patients who underwent isolated type 1 BAV repair with either internal or external suture annuloplasty. Each group included 10 patients with comparable clinical features. Preoperative and postoperative ECG-gated CT scans were performed to assess the anatomical relationship between the ventricular-aortic junction (VAJ) and virtual basal ring (VBR), and to measure the height of annuloplasty from the VBR at predefined landmarks in both groups. Perioperative annular geometries, including annular area and perimeter, were measured to quantify the impact of annuloplasty on annular expansibility. The discrepancy between the postoperative annular dimension and size of the Hegar dilator were compared between groups to evaluate the effectiveness of annuloplasty. Results: In both groups, VAJ was higher than VBR at the right coronary (RC) ostium (7.7 \pm 3.3 mm) and the raphe (7.9 \pm 1.5 mm). The height from the VBR to the external suture annuloplasty shared a similar pattern at the RC ostium and raphe (5.3 \pm 1.1 mm and 4.8 \pm 1.0 mm, respectively). In contrast, the height differences were minimal for these landmarks in the internal group. Postoperative annular area expansibility decreased in the internal group compared to preoperative levels (4.9 \pm 2.3% vs. 8.9 \pm 5.5%, p = 0.038), while no significant change was found in the external group (7.6 \pm 4.1% vs. 6.5 \pm 2.8%, p = 0.473). The internal group showed less area discrepancy between the VBR and the Hegar dilator both at systole (10.1 \pm 3.7% vs. 30.1 \pm 16.6%, p = 0.004) and diastole (5.7 \pm 4.9% vs. 20.9 \pm 14.5%, p = 0.009) compared to the external group. Conclusions: Internal suture annuloplasty results in better positioning relative to the VBR than external suture annuloplasty due to the absence of VAJ interference. While this results in more precise annular reduction and less expansibility in the short term, a long-term follow-up evaluation is necessary to assess its effectiveness.