A group of 44 patients with idiopathic scoliosis (mean age 13.6 years) with an initial Cobb angle between 20° and 32° received side-shift therapy (mean treatment duration 2.2 years). A group of 120 brace patients (mean age 13.6 years) with an initial Cobb angle in the same range (mean brace treatment 3.0 years) was the historical reference group. Failure was defined as an increase of Cobb angle greater than 5° within 4 months or a Cobb angle greater than 35° or a total increase of Cobb angle greater than 10°. The chance of success was not significantly different between the side-shift and the brace groups, whether tested for efficiency (66% vs 68%) or efficacy (85% vs 90%). The difference in the mean progression of the Cobb angle for the respective groups is small (for efficiency: 3° vs –2°, for efficacy: 2° vs –1°). Side-shift therapy appears to be a promising additional treatment for idiopathic scoliosis in adolescents with an inital Cobb angle between 20° and 32°.