Breast asymmetry is frequent in women with idiopathic scoliosis. To understand the pattern of breast asymmetry in these women a clinical study was performed in which 54 female patients with idiopathic scoliosis were evaluated. The information recorded for each patient included: age, weight, height, scoliosis type, Cobb angle, breast measurements, and presence of rib cage asymmetry. Breast volume was calculated using anatomic measurements (anthropomorphic method). The mean age of the group was 25 +/- 7 years. A right convex thoracic curve occurred in 85%, with a mean Cobb angle of 32 +/- 15 degrees. Our study indicated that women with idiopathic scoliosis consistently presented breast asymmetry that followed a predictable pattern. The breast on the side of the convex thoracic scoliosis curve is always smaller in volume (mean difference 59 +/- 39 mi). The affected side also presents a smaller areola, a higher position of the nipple (mean difference 2.2 +/- 1.3 cm) and a higher position of the inframammary fold (mean difference 2.1 +/- 1.4 cm) when compared to the opposite breast. Though the asymmetry is predictable, the degree to which the patient presents these changes does not correlate with the severity of the scoliosis (Cobb angle). We believe that the severity of the asymmetry is a result of the difference between the hypoplastic breast and the normal breasts. In women with very large opposite breasts the asymmetry appears to be worse.