Abstract Objectives To determine whether two independent examiners can agree on a diagnosis of myofascial pain syndrome (MPS). To evaluate interexaminer reliability in identifying myofascial trigger points in upper quarter muscles. To evaluate the reliability of clinical diagnostic criteria for the diagnosis of MPS. To evaluate the validity of clinical diagnostic criteria for the diagnosis of MPS. Design Validity and reliability study. Setting Provincial Hospital. Toledo, Spain. Participants Twenty myofascial pain syndrome patients and 20 healthy, normal control subjects, enrolled by a trained and experienced examiner. Methods Ten bilateral muscles from the upper quarter were evaluated by two experienced examiners. The second examiner was blinded to the diagnosis group. The MPS diagnosis required at least one muscle to have an active myofascial trigger point. Three to four days separated the two examinations. The primary outcome measure was the frequency with which the two examiners agreed on the classification of the subjects as patients or as healthy controls. The kappa statistic (K) was used to determine the level of agreement between both examinations, interpreted as very good (0.81–1.00), good (0.61–0.80), moderate (0.41–0.60), fair (0.21–0.40), or poor (≤0.20). Results Interexaminer reliability for identifying subjects with MPS was very good (K = 1.0). Interexaminer reliability for identifying muscles leading to a diagnosis of MPS was also very good (K = 0.81). Sensitivity and specificity showed high values for most examination tests in all muscles, which confirms the validity of clinical diagnostic criteria in the diagnosis of MPS. Conclusions Interrater reliability between two expert examiners identifying subjects with MPS involving upper quarter muscles exhibited substantial agreement. These results suggest that clinical criteria can be valid and reliable in the diagnosis of this condition.