This study aims to evaluate the thickness of the abdominal muscles on both sides in patients with mild adolescent idiopathic scoliosis (AIS) and to assess the absolute and relative thickness of oblique external (OE), oblique internal (OI), and transversus abdominis (TrA).A total of 84 participants underwent ultrasonographic examination of the abdominal muscles in the supine resting position. All participants were divided into two groups including AIS group (n=42) and control group (n=42). The absolute and relative thicknesses of OE, OI, and TrA were recorded.In the AIS group, the TrA on the left side was significantly thicker by 0.30 mm (95% CI 0.01-0.7) than the right side. For relative values, the percentage contribution to the structure of the lateral abdominal wall of the OE on the right and the TrA on the left was significantly higher by 3.2% (95% CI 0.9-5.5) and 3.1% (95% CI 1.1-5.0), respectively, in the AIS group.Our study results show that, in the supine resting position, the muscles of the lateral abdominal wall are thinner in AIS patients. In addition, side-to-side differences in the percentage contribution of the OE and TrA to the structure of the lateral abdominal wall are seen in this patient population, although these differences are independent of the direction of the scoliosis.