Whether acetabular volume increases or decreases after acetabular Dega osteotomy is not known. The purpose of this study is to determine the effect of Dega osteotomy on the volume of the acetabulum in patients with developmental dysplasia of the hip. Nine hips of seven patients with developmental dysplasia of the hip that have undergone Dega osteotomy were included in the study. The acetabular index, acetabular depth, and acetabular volume of each hip were calculated before and after surgery. Magnetic resonance imaging was used for the measurement of the acetabular volume. The difference between the preoperative and postoperative values of acetabular index, acetabular depth, and acetabular volume was statistically significant. We conclude that Dega acetabular osteotomy increases the volume of the acetabulum.