Current treatment for head and neck cancers (HNCs) have led to an improved survival. However, the sequelae of cancer treatment often result in trismus, or reduced mouth opening. The purpose of this report is to identify interventional studies for trismus management in HNC patients. A search of PubMed, Embase, Cumulated Index to Nursing and Allied Health Literature, and the Cochrane Library was conducted in March 2020 for randomized controlled trials (RCTs) involving interventions for trismus for head and neck cancer within 10 years. Intervention could involve the use of an exercise regime, jaw rehabilitation device, technological device, medication or massage therapy. The primary outcome was the measurement of mouth opening. Eleven RCTs involving a total of 685 patients with HNC were included. Six RCTs evaluated the effectiveness of a jaw mobilization device with exercises; there was no significant benefit of an exercise regime with a jaw mobilization device either initiated before, during or after treatment compared to no exercise. Two RCTs compared 2 intervention groups that involved exercises only, with 1 study assessing the benefit of weekly supervised physical therapy with gum chewing and another evaluating the benefit of immediate (1-2 days) versus delayed (7-10 days) initiation of exercise post-surgery; there was no significant difference between groups in either study. One RCT that recruited only patients with trismus demonstrated that an exercise regime in combination with low-level laser therapy or low-intensity ultrasound had superior results in mouth opening measurements compared to exercise alone. Two RCTs compared intervention groups with and without follow-up reminders; both studies showed a significant improvement in mouth opening measurements in groups with follow-up reminders. This systematic review did not convey a clear consensus as to optimal intervention for trismus in HNC patients. A variety of exercise regimens and jaw rehabilitation devices appear to have comparable effectiveness. However, efforts focused on increasing adherence to a particular intervention protocol may positively impact mouth opening measures in head and neck cancer patients. Also, low-level laser therapy and low-intensity ultrasound coupled with exercise may be beneficial for patients with trismus.