Acetabular redirection osteotomy can be used to relieve pain, improve function, and extend the life of dysplastic hip joints. To understand better the factors that may determine the acetabular reorientation that minimizes pressures, joint contact pressures were calculated by computer assisted methods in 70 dysplastic and 12 normal hips (82 patients). Calculated pressures were consistent with pressures estimated and measured by other investigators. Contact areas were 26% smaller, and contact pressures were 23% higher, in the dysplastic hips compared with the normal hips. When the acetabula were reoriented to minimize contact pressures for an activity such as the midstance phase of gait, then contact pressures were elevated for dissimilar activities such as stair ascent. Contact pressures in the dysplastic hips were reduced when the acetabula were rotated in the frontal plane to increase lateral coverage or rotated in the sagittal plane to increase anterior coverage. In most of the dysplastic hips, contact pressures were reduced twice as much when the acetabulum was rotated in the frontal and the sagitta' planes. Computer assisted methods to quantify joint contact pressures can be used to assess potential candidates for reconstruction, plan acetabular redirection surgery, and possibly may improve the long term success of acetabular redirection osteotomy.