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This study was undertaken to determine the validity and reliability of the physical examination tests commonly used to measure hip flexion contracture in patients with cerebral palsy who are able to walk.Thirty-six consecutive patients (twenty-two male and fourteen female patients), with a mean age (and standard deviation) of 9.8 ± 3.9 years, who had cerebral palsy (level I, II, or III on the Gross Motor Function Classification System) and thirty-seven children without cerebral palsy (nineteen male and eighteen female subjects), with a mean age of 10.0 ± 3.0 years, were enrolled prospectively for this study. Hip flexion contracture was determined by three physical examination tests: the Thomas test, the prone hip extension test (the Staheli test), and the hamstring shift test. Three-dimensional gait analysis was performed in all subjects. The interobserver reliabilities of the three physical examination tests were determined with use of three observers. Convergent validity was assessed by evaluating the relationships between the findings on physical examination and kinematic and kinetic gait variables (maximum hip extension during stance and hip flexor index) and three-dimensional modeled psoas lengths.The Thomas test showed the highest intraclass correlation coefficient (0.501 in patients and 0.207 in controls) and the smallest mean absolute difference (5.8° in patients and 1.2° in controls). The Staheli test was found to be the most valid method in the patient group (r = 0.568 with hip flexor index), whereas the Thomas test was the most valid in the control group (r = 0.526 with maximum hip extension in stance, and r = 0.532 with the hip flexor index). The hamstring shift test had the lowest intraclass correlation coefficient and the lowest convergent validity.While the Thomas test showed the highest intraclass correlation coefficient and the smallest mean absolute difference, the Staheli test was the most valid method for detecting hip flexion contractures in patients with cerebral palsy. Although the Staheli test cannot be used for intraoperative assessment, we recommend that this test be included in preoperative physical examinations to determine the role of a hip flexion contracture in the abnormal gait of patients with cerebral palsy.