Deep paravertebral muscles and female sex hormones are potential elements participating in idiopathic scoliosis development. Estrogen acts through estrogen receptors: ESR1 and ESR2. There are no studies describing ESR2 expression in back muscles in girls with idiopathic scoliosis. The aim of this study was to evaluate ESR2 expression levels in back muscles on both sides of the spinal curve and correlation between the expression level and scoliosis parameters. Asymmetrical ESR2 expression in deep paravertebral muscles was found: 11 girls had higher expression level on the convex side and 5 girls had higher expression level on the concave side of the curvature. Patients with ESR2 (convex/concave) ratio ≥ 1 presented positive correlation between ESR2 ratio and Cobb angle.