OBJECTIVE To examine the intra- and intertester and intra- and interday reliability of hip passive range of motion (PROM) measurements and the effect of passive stretch on the reproducibility of PROM measurements. METHODS Reliability study. METHODS Rehabilitation clinic at university hospital. METHODS Twenty volunteers (12 women, 8 men; age range, 18-45 y). METHODS Not applicable. METHODS Two physical therapists made 2 PROM measurements on the first day and repeated them once after 2 days. The PROM in hip flexion, extension, and inner rotation and knee flexion were determined. The measurements of the hip flexion and inner rotation involved either 1 or 8 short-term passive stretches. The reproducibility was expressed as the intraclass correlation coefficient (ICC) and the coefficient of variation (CV) (in percent). RESULTS The passive stretch increased significantly ( P <.05 to P <.001) the PROM of the hip joint. The reproducibility of the PROM measurement did not increase after repetitive passive stretch. The intra- and interday intra- and intertester ICC and CV of the PROM of the hip flexion and hip inner rotation ranged from .655 to .988 and 2.1% to 12.6%, respectively. The intra- and intertester intra- and interday ICC of the PROM of the hip extension ranged from .740 to .961, and the CV ranged from -85.5% to 242.6%. The intra- and intertester intra- and interday ICC of the PROM of the knee flexion ranged from .497 to .913, and the CV ranged from 2.5% to 9.9%. CONCLUSIONS Repetitive stretching increased significantly the PROM in hip flexion and inner rotation, but the reproducibility of the PROM measurement did not improve. The hip flexion and the hip inner rotation PROM measurements had moderate to very high intra- and interday intra- and intertester reliabilities. The reliability of the PROM in hip extension and knee flexion was poor.