The purpose of this study was to use MRI to classify acute grade one hamstring muscle strains in Australian Rules footballers to determine if it was accurate in predicting the recovery time for each injury and also able to predict those that would recur within the same season. A prospective study was performed over five years at a professional Australian Football League club. Thirty-one acute grade one hamstring injuries underwent MRI examination within 24-72 hours following the injury. Each injury underwent the same rehabilitation programme. The rehabilitation interval (RI) was the time in days for the player to resume full team training. Fourteen (45%) of the injuries were normal on MRI. Seventeen (55%) were abnormal with a hyperintense T2 lesion on the axial fat suppressed views. The MRI negative group had a significantly faster RI (6.6 days) compared with the MRI positive group (20.2 days). Both the length and cross sectional area (CSA) of the MRI positive lesions were measured. The length of the lesion had a stronger correlation coefficient with the RI (0.84) than did the CSA (0.76). Six of the 17 MRI positive strains recurred with no correlation found between the lesion's length or CSA, or the RI. None of the 14 MRI negative injuries recurred. The study confirms that MRI can aid in the investigation of acute grade one hamstring muscle strains in predicting recovery time. However the size of the initial strain or the RI do not seem to be reliable indicators in predicting those strains that might recur.