Background: Universal clinical screening for congenital dislocation of the hip to detect hip instability in neonates was introduced in the UK as a national policy in 1969, but its effectiveness is not known. We aimed to assess the extent to which surgery for congenital dislocation of the hip is the result of a failure of detection through screening or follows non-surgical treatment after detection by screening., Methods: We established a national orthopaedic surveillance scheme and used routine hospital data for inpatients for 20% of births in the UK (Scotland and the Northern and Wessex regions) to ascertain the number of children aged under 5 years per 1000 livebirths who had received at least one operative procedure for congenital dislocation of the hip from April, 1993, to April, 1994. Estimates of the incidence of operative procedures were adjusted for under-ascertainment by capture-recapture techniques., Findings: The ascertainment-adjusted incidence of a first operative procedure for congenital dislocation of the hip in the UK was 0.78 per 1000 livebirths (95% CI 0.72-0-84). Congenital dislocation of the hip had not been detected by routine screening in 222 (70%) of 318 children reported to the national orthopaedic surveillance scheme. In 112 (35%) children the diagnosis was made primarily as a result of parental concern. 67 (21%) children had previously received non-surgical treatment. In Scotland and the Northern and Wessex regions, 81 cases were notified to the national orthopaedic surveillance scheme, 62 cases were identified only through routine hospital data on inpatients, and an estimated 20 cases were not identified by either source, making a total of 163 cases. Thus, 81 (50%) of these 163 cases were identified by surveillance, 125 (77%) by routine data, and 143 (88%) by both sources., Interpretation: The incidence of a first operative procedure for congenital dislocation of the hip in the UK was similar to that reported before screening was introduced. In most children who received surgery, congenital dislocation of the hip was not detected by screening. Formal evaluation of current and alternative screening policies, including universal primary ultrasound imaging, is needed. more...