BaCKGROUND: Periacetabular osteotomy improves radiographic predictors of osteoarthrosis and diminishes pain and functional impairment. No changes in function quantified by gait analysis have yet been documented. We evaluated the functional outcome of periacetabular osteotomy in relation to gait. METHODS: The gait pattern of 9 women (median age 39 years) with hip dysplasia who were treated with unilateral periacetabular osteotomy was analyzed before periacetabular osteotomy and an average of 1.5 years afterwards. Data were collected using 5 video cameras and 2 force plates. An inverse dynamics approach was used to calculate sagittal joint angles and moments in the stance phase. RESULTS: Postoperatively, all subjects walked with an increased extension of the knee joint during the entire stance phase compared to the preoperative movement pattern. INTERPRETATION: The subjects achieved a more upright walking pattern but continued to relieve the hip joint by maintaining a reduced flexor moment.