Eight consecutive patients, mean age 17.25 years, underwent a medial displacement osteotomy and hip arthrodesis with a nine-hole Cobra plate. A transverse innominate osteotomy facilitated medial displacement of the femoral head and acetabulum. Alignment of the lower limb at 25 degrees flexion, neutral abduction, and neutral rotation was assisted by a long-limbed protractor and Steinmann pins placed in both anterior superior iliac spines. The greater trochanter was reattached to the Cobra plate so that hip abductor function could be restored should the fusion ever be converted to an arthroplasty. No postoperative immobilization was required. All patients had radiographic evidence of union by 12 months. One patient had a postoperative brachial plexus neuropraxia that resolved at three months. One patient required an ipsilateral femoral lengthening for limb-length inequality secondary to collapse of his femoral head before hip fusion. At a mean follow-up interval of 2.8 years (range, one to 4.5 years), all patients had significant improvements in pain (p < 0.05), function (p < 0.01), and gait (p < 0.01). The average preoperative Harris Hip Score of 45 points +/- 8 points (mean +/- SEM) improved to 84 points +/- 2 points (p < 0.01).