Grindcare^® (Medotech, Copenhagen, Denmark) is a biofeedback device that combines electromyographic (EMG) measurements and electrical responses after recorded muscle contractions. The device is advertised for its reduction of sleep bruxism and related symptoms. The aim of this study was to measure EMG activity in patients with myofascial pain and to test if the device reduces EMG activity and symptoms of myofascial pain. Forty-eight patients with complaints of myofascial pain were invited for the study and divided randomly into two groups. The treatment group received instructions, EMG measurement and treatment with electrical stimulation. The control group received instructions and EMG measurement only. EMG measurements were recorded for 4 weeks. Pain assessment was performed at baseline, after 1 week, 3 weeks and 5 weeks after beginning of measurements using an numerical analog scale (NAS) for pain intensity, pain frequency, degree of limitation and restriction of daily life. Furthermore, clinical functional examination was performed. An analysis of variance (ANOVA) and a Wilcoxon Test were applied for statistical analyses. After 3 weeks of application of the active device, the number of EMG events/h dropped from 96.72 (± 57.81) to 33.57 (± 23.98). The controls exhibited 75.80 (± 59.00) EMG events/h at baseline and after 4 weeks, the measurement was 70.25 (± 50.40) EMG events/h (P = 0.02). Clinical data recording the pain intensity, the extent of daily life restrictions as well as the number of painful muscles on palpation, which did not differ significantly between groups at any examination (P > 0.05). In the treatment group, however, significant differences between baseline examination and examination after 5 weeks were observed for pain intensity (P = 0.001), daily life restrictions (P = 0.001) and number of painful muscles on palpation (P 0.001). Within the limitations of this observational study, it was demonstrated that in patients with myofascial pain, EMG events/h of the temporalis muscle were significantly reduced after 3 weeks of therapy with electrical stimulation of this muscle. Keywords: biofeedback, myofascial pain, sleep bruxism, temporomandibular disorders