In hips with acetabular dysplasia, we performed Kotz osteotomy (group 1) in 22 hips (20 patients; mean age 24.3 years) and Ganz osteotomy (group 2) in 23 hips (22 patients; mean age 23.1 years). Group 1 was followed 83.3 (56-112) months and group 2 40.9 (24-66) months. In group 1, Harris hip score improved from average 74.9 to 86.9, mean center edge (CE) angle from -4.5degrees to 30.3degrees, and mean vertical center edge (VCE) angle from 5.3degrees to 36.2degrees. In group 2, Harris hip score improved from average 76.6 to 91.1, mean CE angle from -5.9degrees to 32.0degrees, and mean VCE angle from 5.0degrees to 41.3degrees. Using Pauwels criteria, regression was observed in 12 hips in group 1 and one progressed. In group 2, 15 hips showed regression and three progressed. In patients treated with Ganz osteotomy, the complication rate was higher and the complications more serious than in patients treated with Kotz osteotomy. Most complications were, however, seen among the first ten patients treated with Ganz osteotomy. Although we detected no significant difference between the two groups in terms of clinical and radiological findings, we believe the outcome to be slightly better after a properly performed Ganz osteotomy.