Abstract Purpose We determined the relationship between hamstring injury and hamstring length in a prospective analysis of adolescent football players as well as assessing the impact of age and test type upon hamstring length. Method One hundred and eleven footballers (9–19 years old) volunteered after subject and parental/guardian consent. Hamstring muscle length was assessed at baseline via; modified sit-and-reach (mSAR), straight leg raise (SLR), active knee extension (AKE), passive knee extension (PKE) and seated knee extension (SKE). Medical staff recorded hamstring injuries during the following competitive season. Results During the study 16 subjects reported 20 hamstring strains. Data for all hamstring muscle length tests were not significantly different ( P >0.01) between injured and non-injured legs (e.g. SLR 73.3±7.0° vs. 74.3±7.5°) or between injured and non-injured subjects (e.g. SLR right leg 74.3±7.9° vs. 76.9±9.8°, SLR left leg 73.8±5.9° vs. 74.7±9.3°). Data for hamstring length across age groups significantly declined ( P P r =0.55–0.87), whereas mSAR was only weakly correlated with other tests ( r =−0.01 to −0.27). Conclusion Hamstring injuries are common in young footballers and are not overtly related to significant decrements in hamstring muscle length, although individual case analysis may be advisable. Estimates of apparent hamstring muscle length differ dependent on age and on the test employed.