ABSTRACT Although the diaphragmatic release technique is used a lot in clinical practice, there is no previous study demonstrating the effect of this technique on patients with upper-crossed syndrome. The aim of this study was to investigate the effect of diaphragmatic release on neck pain and chest expansion in upper-crossed syndrome patients. A prospective parallel randomized control trial study of 30 patients with upper crossed syndrome aged 20 to 26 years was divided into two equal groups: intervention and control groups.  Both groups received the same posture correction exercise, while the intervention group had an additional diaphragmatic release technique three times per week for four weeks. Neck pain intensity, chest expansion, and forward head posture angle were measured using a visual analog scale, tape measurement, and craniovertebral angle. The obtained results showed that there was no statistically significant difference between the groups' pretreatment (p > 0.05) in the three measured parameters. Post-treatment, there was a statistically significant decrease in VAS and a statistically significant increase in chest expansion of the intervention group compared with the control group (p < 0.001), but there was no statistically significant difference in craniovertebral angle (p > 0.05). It could be concluded that adding the diaphragmatic release technique to exercise improves chest expansion and neck pain in patients with upper crossed syndrome. This technique should be considered in the management of people with the upper-crossed syndrome.