Background: Despite the increasing use of diaphragm myofascial release technique in clinical practice, there is no study on the effect of this technique on musculoskeletal outcomes of patients with neck pain. The purpose of this study was to evaluate the added value of diaphragm myofascial release on forward head posture, chest expansion, and functional disability in patients with neck pain.Methods: In this randomized controlled trial, 46 women with neck pain between the age of 18 and 45 years old were randomly allocated to two groups; the intervention group received 4 diaphragm myofascial release techniques once a week, for 4 weeks. Both intervention and control groups received the same neck exercise program 3 times a week for 4 weeks. Forward head posture, chest expansion, and neck functional disability were measured using craniovertebral angle, circometry, and Copenhagen neck functional disability index, respectively, before and one day after treatment.Results: The results of the paired t-test showed significant increases in craniovertebral angle (control and intervention: P<0.001) and chest expansion (control: P=0.001, intervention<0.001) and a significant decrease in the functional disability score (control and intervention: P<0.001) of patients with neck pain in both groups. A significant greater craniovertebral angle (P=0.01) and chest expansion (P=0.03) were also seen in the intervention group compared with the controls.Conclusion: Adding diaphragm myofascial release to neck exercises was associated with significantly greater improvements in forward head posture and chest expansion than neck exercises alone. Therefore, the diaphragm myofascial release could be useful in the management of neck pain patients with FHP. Trial registration: IRCT20191116045461N1 (Iranian Registry of Clinical Trials). Registered 23 December 2019, https://en.irct.ir/trial/43741.