Metal-on-metal hip resurfacing was performed for developmental dysplasia in 96 hips in 85 patients, 78 in women and 18 in men, with a mean age at the time of surgery of 43 years (14 to 65). These cases were matched for age, gender, operating surgeon and date of operation with a group of patients with primary osteoarthritis who had been treated by resurfacing, to provide a control group of 96 hips (93 patients). A clinical and radiological follow-up study was performed. The dysplasia group were followed for a mean of 4.4 years (2.0 to 8.5) and the osteoarthritis group for a mean of 4.5 years (2.2 to 9.4). Of the dysplasia cases, 17 (18%) were classified as Crowe grade III or IV. There were five (5.2%) revisions in the dysplasia group and none in the osteoarthritic patients. Four of the failures were due to acetabular loosening and the other sustained a fracture of the neck of femur. There was a significant difference in survival between the two groups (p = 0.02). The five-year survival was 96.7% (95% confidence interval 90.0 to 100) for the dysplasia group and 100% (95% confidence interval 100 to 100) for the osteoarthritic group. There was no significant difference in the median Oxford hip score between the two groups at any time during the study. The medium-term results of metal-on-metal hip resurfacing in all grades of developmental dysplasia are encouraging, although they are significantly worse than in a group of matched patients with osteoarthritis treated in the same manner.