Introduction: The most common way of measuring joint mobility is goniometric measurements. Measurements are performed with a universal goniometer. We carry them out in order to obtain objective measurements of the flexibility of a particular joint. Because measurements are usually conducted by different therapists, the intratester reliability is very important. Purpose: The purpose of the diploma thesis was to identify the repeatability and reliability of passive goniometric measurements of the range of flexibility of the knee joint. Methods: The study involved 30 healthy subjects aged between 18 and 25 years. Measurements were made in two sessions with a 48 hours intermittent break. The differences between the measurements were assessed by the analysis of the variance for repeated measurements (p≤0.05), if the difference between the measurements was significant, we performed the "post hoc" test of Bonferroni (p≤0.05). Repeatability and reliability were assessed by the intraclassic correlation coefficient (ICC 2.1). We also calculated the lowest real difference. MedCalc Statistical Software version 14.12.0 (MedCalc Software bvba, Ostend, Belgium) and Microsoft Excel (version 2013, Microsoft Corporation, Redmond, USA) was used to process data. Results: Thus, in the first, as in the second session, there were no significant differences between the initial measurements of the initial and final positions. The repeatability of the test was high. The highest ICC was calculated for extensions measurements (ICC = 0.935) and the lowest in the first measurements of flexion (ICC = 0.808) in the first session. The average values of measurements between the first and frugo sessions were important only for extensions measurements (p = 0.013). ICC values for all measured variables above 0.8, indicating the excellent reliability of the method. Reliability was better in the measurement of fleshes (ICC = 0.925). The slightest actual difference was in the measurements of the extension of 4.3°, in the measurements of the flexion 4.0° and for the entire range of movement 6.0°. Discussion and conclusion: Goniometric measurements of the knee joint are repeatable and reliable, somewhat more in the measurement of flexion than in the measurement of the passive motion of the knee joint extension. Reliability is comparable to other studies already carried out. The smallest detected change also indicates excellent reliability. Compared to already performed studies, the smallest reliable change in our study is even lower.