Few studies have investigated the reliability of Reimers’ hip migration percentage (RMP) in children with cerebral palsy (CP). Most studies on the topic reflected rating results of physician with a similar level of experience from the same expertise. This study aimed to determine the effect of clinician’s experience and expertise on the intra-and inter-observer reliability of RMP.In this retrospective observational study, hip radiographs of children with CP were identified. 5 observers with different degrees of working experience from 3 different clinical fields, including orthopedics, radiology, and physical medicine and rehabilitation, performed all RMP measurements. All measurements were repeated 6 weeks later by the same observers. Inter- and intra-observer reliability for RMP measurements were assessed using Intraclass Correlation Coeficient (ICC), calculated from 2 sets of repeated measurements on a subset of 50 hips, with a 6 week apart for each observer.Fifty hip radiographs of 25 children with CP (10 females and 15 males; mean age: 6 years; age range: 2-8 years) were examined in the current study. No significant differences existed in intra-and inter-observer measurements. Excellent intra-observer reliability was observed between the 2 separate measurements for each observer, with a mean ICC of 0.976 (range: 0.956-0.989; P < .001). Among 5 observers, inter-observer reliability was excellent for the 2 separate RMP measurements, with the mean ICC minimally increasing between the 2 measurement periods (mean ICC: 0.928, range: 0.838-0.979 and mean ICC: 0.936, range: 0.861-0.983, respectively) (P < .001).Clinician's experience and expertise may not affect inter-and intra-observer reliability of RMP measurements.