To determine the incidence of congenital hip dislocation (CDH) a retrospective study was carried out of cases occurring in a defined population using multiple information sources. Of 138 600 children born in the period 1983-1987, a total of 243 were diagnosed with CDH, defined as those requiring splintage or surgery whose treatment extended beyond 6 months of age. Incidence and estimates of relative risks for pre-disposing factors were determined. The rate was 1.75 cases per 1 000 livebirths. Major risk factors were female gender and breech presentation. The proportions of cases identified before 1, 3 and 6 months of age were 8, 14 and 35%, respectively. Despite using a restrictive definition, we have obtained an incidence rate among the highest reported in any United Kingdom population. Early detection is widely accepted as desirable, but neonatal screening has proved ineffective.