Ultrasound investigation of the hip according to Graf is performed, whenever possible, as a routine screening test for hip dysplasia and dislocation in neonates. However, in spite of screening, hip dysplasia and/or dislocation is identified in a number of children after the third month of life only. The present study presents an analysis of reasons and causes. Between August 1999 and July 2001 children aged between six months and five years were documented, in whom the diagnosis of hip dysplasia or dislocation was made, despite normal ultrasound findings at primary investigation and who required non operative or operative treatment by a specialist surgeon working in Switzerland in paediatric orthopaedics. The study included 26 children (17 girls / 9 boys). Hip dysplasia and/or dislocation was diagnosed between the age of 6 days and 41 months. Twelve children had to be excluded from the sample (n = 26), four were infants who had basic neurological disorders or multiple anomalies and there were eight children from abroad whose original documentation could not be obtained. Analysis of the remaining 14 children showed that 43% were misdiagnosed (n = 6) and a treatment error occurred in 36% (n = 5) of cases. One child presented with a teratogenic hip dislocation. In two other infants with normal primary ultrasound findings, hip dysplasia was identified radiographically once the child started to walk. Delayed diagnosis can be the result of technical errors or misinterpretation. The six patients meeting the criteria of misinterpretation can be expressed as a rate of 0.04% of all births. However, even if the disorder is correctly diagnosed, its identification and treatment may be inadequate or fail to produce the desired results. This was the case for five of the children, that is, for a rate of 0.03% of births.