Background: Hamstrings are one of the most frequently evaluatedmuscle groups for flexibility in the lower extremity. Passive andactive knee extension angle values are used as an indirect indicatorof hamstring flexibility. However, the lack of consensus on the cut-offvalues leads to the use of inconsistent angle values in determining thehamstring tightness.Aims: To establish the normative and cut-off values of the passiveand active knee extension angles for healthy young adults and todetermine the associated factors including the quadriceps strength.Study Design: A cross-sectional study.Methods: A total of 123 volunteer university students, aged 18-24years, who met the inclusion criteria were included in this study.Passive and active knee extension assessments of the subjectswere performed. Subsequently, on the next day, both knee extensorconcentric muscle strength of the participants was measured in theisokinetic system. The knee extension angles and the knee extensorstrength were recorded as the mean values of the right and the leftsides.Results: Passive knee extension angles of 17.1°±9.1° and 9.8°±5.7°and active knee extension angles of 17.8°±9.1° and 13.4°±6° weredescribed as normative values in men and women, respectively.The cut-off values for the diagnosis of hamstring shortness were asfollows: passive knee extension angle >32.2° for males and >19.2° forfemales and active knee extension angle >33.0° for males and >23.4°for females. A significant positive correlation was observed betweenknee extension angles and isokinetic knee extensor muscle strengthin all participants. The knee extension angle and hamstring flexibilitywere not affected by dominance.Conclusion: The knee extension angles of healthy young people seemto be lower than the results currently reported in the literature. Theres a positive correlation between knee extension angles and isokineticknee extensor muscle strength.