Introduction The Trunk-Pelvis-Hip Angle (TPHA) test is used for assessing the mobility of lumbo-pelvic-hip complex. The aim of the research was to assess the intraobserver reliability of the TPHA test in girls with and without idiopathic scoliosis and to compare the test values obtained by the girls in both groups. Material and methods The research included girls without scoliosis and girls with double idiopathic scoliosis aged 8-16. The trunk-pelvis-hip angle was measured three times on each body side within one session. Statistical analysis was performed with the use of ANOVA intraclass correlation coefficient for dependent groups, Kolmogorov-Smirnov test as well as non-parametric Wilcoxon signed-rank test for dependent groups and Mann-Whitney U test for independent groups. Results The research included 49 healthy girls (aged 11.8 ± SD 2.5 years) and 49 girls with double idiopathic scoliosis (aged 12.7 ± SD 2.6 years; Cobb angle Th 27.7º ± SD 13.4º and L Cobb 25.8º ± SD 10.5º). The intraobserver reliability for the TPHA measurements was very high (ICC>0.85). In both groups the left-side TPHA value was significantly higher than the right-side value (p=0.001). The TPHA range of motion on the right side of the body was more limited in the scoliotic girls than in the healthy ones (p=0.001). Conclusions The TPHA test is a reliable means of assessing mobility in the lumbo-pelvic-hip complex in girls by one observer.The asymmetry of movements in the lumbo-pelvic-hip complex in healthy girls needs to be observed since it may constitute one of the factors predisposing to scoliosis which limits spine rotation range of motion. The TPHA test needs further research.