Aims: To prospectively evaluate the effectiveness of a treatment regimen comprising counseling and physical therapy in patients with myofascial pain of the masticatory system, and to explore whether the duration of the physical therapy offered (4 vs 6 weeks) would influence the treatment result. Methods: Twenty-six patients were randomly distributed over 2 groups. All patients received reassuring information, advice regarding relaxation of the jaws, avoiding parafunctions, and limited use of the jaws. In addition, a physical therapy program (heat application, massage, ultrasound and muscle stretching) was initiated 2 weeks after the start of the study (group I, receiving 4 weeks of physical therapy) or immediately from the start of the study (group II, receiving 6 weeks of physical therapy). The following parameters were taken at baseline, 2, 4, and 6 weeks: visual analog scale (VAS) scores of present pain; lowest and highest pain over the past period; percentage of pain relief; jaw function assessment by the Mandibular Function Impairment Questionnaire (MFIQ); and pressure pain thresholds (PPTs) of the masseter, temporalis, and thumb muscles. Statistical analysis used a linear mixed model and corrected for multiple testing (Tukey test). Results: Pain and MFIQ scores decreased while PPTs increased in both groups. Only after 4 and 6 weeks, significant differences were present for the PPT of the masseter in group I (P .02) and the temporalis in both groups (P .01). Also, the VAS scores of present (P .02), minimal (P .01), and maximal (P .0001) pain and the MFIQ score (P .001) improved. After 6 weeks, a mean of 60% pain decrease was reported (P .0001). There were no significant differences between the groups receiving 4 weeks vs 6 weeks of physical therapy. Conclusion: A conservative approach involving counseling and physical therapy resulted in significant improvement in parameters of pain and jaw function in patients with myofascial pain. A controlled study will be necessary to elucidate the specific effectiveness of physical therapy over counseling or no treatment. Palabras clave: temporomandibular disorders, treatment, physical therapy