Purpose To analyse the consequences of using different radiographic measurements and different threshold values for hip screening in children with cerebral palsy (CP).Methods In a total sample of children with CP a standardised radiological follow-up of the hips was carried out as a part of a hip prevention programme. Acetabular index (AI) and migration percentage (MP) were measured on all radiographs. In this study, 1,067 radiographs of 272 children born 1992-1998 were analysed. Results Lateral displacement of the femoral head was common without acetabular dysplasia, and acetabular dysplasia occurred at a later stage than femoral head lateralisation. Hip dysplasia without lateral displacement of the femoral head was rare. In 16 of the 56 hips (29%) with AI ‡ 27°and in 23 of the 71 (32%) hips with MP ‡ 33% the values decreased below the threshold value without operative treatment. In hips with AI ‡ 30°only 2 of 31 hips (6%) and in hips with MP ‡ 40% only 5 of 44 hips (11%) decreased below the threshold values without operative treatment. Conclusions Radiographic follow-up with only measurement of the MP seems sufficient in screening for dislocation in children with CP. MP ‡ 33% is recommended as threshold for reaction or intensified observation. In children with MP ‡ 40%, the lateral displacement increased over time in most hips, thus indicating the need for operative intervention. In children with MP 33-40%, treatment should be based on other clinical signs and the progression of MP over time.