Aims: To evaluate the influence of the menstrual cycle on pressure- pain thresholds (PPTs) in patients with masticatory myalgia. Methods: Fluctuations in pain sensitivity during 2 consecutive menstrual cycles were assessed in 15 normally menstruating patients with a myogenous temporomandibular disorder (TMD). Muscle pain was measured by the use of pressure algometry and a visual analog scale (VAS). The McGill Pain Questionnaire was used to assess the sensory, affective, and evaluative dimensions of the pain. Results: Since 5 patients dropped out of the study due to pregnancy, unexpected menstrual cycle irregularities, or personal problems, statistical analysis was performed on 10 patients. Time had a significant influence on the pain condition. The PPTs of all muscle sites increased significantly and progressively over time by 16% to 42% in the follicular and luteal phases. PPTs remained low in the perimenstrual phase. The VAS pain rating did not correspond well with the PPTs, and the statistical analysis showed that the VAS ratings could not be used as predictors for the PPT measurements or detect the differences between cycle phases. The sensory, affective, and evaluative dimensions of the pain were significantly lower at the end of the trial. Conclusion: These data suggest a significant influence of the menstrual cycle on pain report and a nonspecific improvement of the chronic myogenous TMD. Keywords: pain threshold, menstrual cycle, masticatory muscle, myofascial pain