Objective: Temporomandibular disorders are a group of disorders affecting the temporomandibular joint and/or masticatory muscles. One of the signs associated with temporomandibular disorders is a reduction in mouth opening. During normal mouth opening, extension occurs at the cervical-cranial junction. The purpose of this investigation was to determine if manual therapy applied to the cervical-cranial junction would significantly improve mouth-opening capacity. Methods: One hundred one participants were randomly assigned to either an Active Release Technique (ART) group; high-velocity, low-amplitude manipulation (HVLA) group; or control group. A blinded investigator measured mouth opening using a TheraBite range of motion scale (TheraBite Corporation, West Chester, PA). Participants received ART to the suboccipitals or HVLA to the cervical spine at C1 or sat with an investigator for 3 minutes with no treatment. After the treatment session, mouth opening was remeasured. A repeated-measures analysis of variance was used to compare the group mean values. The a priori α level was .05. Results: The repeated-measures analysis of variance showed no significant difference between the ART, HVLA, and control groups' pretreatment and posttreatment measurements (F = 0.41, P N .05). Conclusion: Manual therapy to the cervical spine did not significantly improve mouth opening in this asymptomatic population. Future trials using participants with restricted mouth-opening measures are warranted.