The purpose of this study was to determine whether differences exist in EMG activity between involved and uninvolved upper trapezius muscles in participants with unilateral neck pain. Thirteen volunteers, seen by a physical therapist, gave informed consent. Surface EMG electrodes were placed on involved and uninvolved upper trapezius muscles. Root mean squared EMG activity was measured. Visual analog scales (VASs) for pain were used for each side. Reliability data indicated high ICC (2,1) but also large SEMs and CVs. EMG activity increased from resting to shrugging to abducting positions. Participants perceived greater pain on the involved side than the uninvolved side. EMG readings for individuals were consistent, however, between participants. EMG had high variability. Although participants' VAS scores were consistent with their reports of unilateral neck pain, surface EMG readings did not support the existence of increased muscle activity on the involved side.