Few studies have reported on the amount of acute changes in flexibility of the hamstrings resulting from stretching prior to activity, and no studies of this nature have focused on an elderly population. Methods: Ninety-seven subjects (mean age=65 years, range 5579 years) participating in the World Senior Games were randomly selected for participation in this study. Subjects were randomly assigned to either a control group (no stretching), or one of two treatment groups (contract-relax proprioceptive neuromuscular facilitation stretch [CRPNF], or a static stretch). Hamstring flexibility was measured with a Penny and Giles goniometer prior to and after one repetition of stretching lasting 32 seconds. Analysis: Differences in flexibility scores from pretest to posttest for control and two treatment groups were assessed using the Wilcoxon signed-ranks test. Pair-wise comparisons in median differences between groups were assessed using rank analysis of covariance and the Mantel-Haenszel statistic. Results: Flexibility scores for participants in each of the control and treatment groups significantly increased from pretest to posttest. However, the increase was much greater for those in the two treatment groups, with median differences of 1 degree in the control group, 5 degrees in the CRPNF group, and 4 degrees in the static group. Both gender and age influenced the median difference between CRPNF and static groups. Specifically, the median difference was significantly greater in the CRPNF versus the static group for men but not women. Similarly, the median difference was significantly greater in the CRPNF versus the static group for participants younger than age 65 but not aged 65 years or older. Conclusion: One repetition (32 seconds) of stretching provides an acute increase in flexibility of the hamstrings. CRPNF and static stretches significantly improve flexibility. For men and participants less than 65 years of age, CRPNF stretch appears more beneficial than static stretch. The benefits in flexibility between CRPNF and static stretches are similar for women and participant ages 65 years and older.