OBJECTIVE To compare a passive and an active stretching technique to determine which one would produce and maintain the greatest gain in hamstring flexibility. To determine whether a passive or an active stretching technique results in a greater increase in hamstring flexibility and to compare whether the gains are maintained. METHODS Randomized controlled trial. METHODS Institutional. METHODS Sixty-five volunteer healthy subjects completed the enrollment questionnaire, 33 completed the required 75% of the treatment after 6 weeks, and 22 were assessed 4 weeks after the training interruption. METHODS A 6-week stretching program with subjects divided into 2 groups with group 1 performing active stretching exercises and group 2 performing passive stretching exercises. METHODS Range of motion (ROM) was measured after 3 and 6 weeks of training and again 4 weeks after the cessation of training and compared with the initial measurement. RESULTS After 3 weeks of training, the mean gain in group 1 (active stretching) on performing the active knee extension range of motion (AKER) test was 5.7 degrees, whereas the mean gain in group 2 (passive stretching) was 3 degrees (P = .015). After 6 weeks of training, the mean gain in group 1 was 8.7 degrees , whereas the mean gain in group 2 was 5.3 degrees (P = .006). Twenty-two subjects were reassessed 4 weeks after the cessation of the training with the maintained gain of ROM in group 1 being 6.3 degrees , whereas the maintained gain in group 2 was 0.1 degrees (P = .003). CONCLUSIONS Active stretching produced the greater gain in the AKER test, and the gain was almost completely maintained 4 weeks after the end of the training, which was not seen with the passive stretching group. Active stretching was more time efficient compared with the static stretching and needed a lower compliance to produce effects on flexibility.