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Background The head-at-risk signs are used as prognostic indicators in Legg-Calvé-Perthes disease. These signs have been assessed only once regarding inter-observer reliability, however. Intra-observer reliability seems not to have been studied to date. Method 76 anteroposterior pelvic radiographs of unilateral Legg-Calvé-Perthes disease were assessed by 5 observers on 2 occasions, in order to assess the inter- and intra-observer reliability in identifying head-at-risk signs. The observers included 1 consultant pediatric orthopaedic surgeon, 1 consultant radiologist, 2 specialist registrars and 1 senior house officer. Inter- and intra-observer reliabilities were assessed using the kappa coefficient. Results The intra-observer reliability was good for lateral subluxation and metaphyseal cystic changes, moderate for lateral calcification, and fair for Gage's sign and horizontal growth plate. The inter-observer reliability was moderate for lateral subluxation, fair for lateral calcification and metaphyseal cystic changes, and slight for Gage's sign and horizontal growth plate. Interpretation There was considerable variation in the diagnosis of the head-at-risk signs between observers. This makes the classification difficult to use in clinical practice. [ABSTRACT FROM AUTHOR]