SummaryStudy aim: To assess the effect of one term of stretching exercise on primary dysmenorrhea in high school students. Material and methods: 179 single girls aged 15-17 years with moderate-to-severe primary dysmenorrhea were selected from 6 high schools located in 2 different city zones. The students were non-athletes and volunteered for the study. The participants were randomly divided into 2 groups: an experimental group (n = 124) and a control group (n = 55). In the intervention group, the subjects were requested to complete an active stretching exercise for 8 weeks (3 days per week, 2 times per day, 10 minutes each time) at home. In the pre-test, all of subjects were examined for pain intensity (10-point scale), pain duration, and the use of sedative tablets in 2 continuous menstruation cycles. The posttest was examined 8 weeks later. Results: After 8 weeks, pain intensity was reduced from 7.65 to 4.88, pain duration was decreased from 7.48 to 3.86 hours, and use of sedative tablets was decreased from 1.65 to 0.79 tablets in the experimental group (p<0.05). In the control group, a significant decline was only noted for pain duration (p<0.001). Conclusions: Stretching exercises are effective in reducing pain intensity, pain duration, and the amount of painkillers used by girls with primary dysmenorrhea.