Background: Mechanical neck pain seen in smartphone addicted population causes respiratory hazards and decrease in peak expiratory flow. Aim: To detect the effect of mechanical neck pain on peak expiratory flow in smartphone addicted population. Methods: 100 volunteers of smartphone addicts with mechanical neck pain were recruited from delta university for science and technology. Their age ranged from 18-25 years. Both sexes were included (47 males, 53 females). Their peak expiratory flow (PEF) was measured using spirometer and the results were compared to the normal predicted values based on age, sex, race, weight and height. Results: there was a significant decrease (P<0.05) in PEF in smartphone addicts with mechanical neck pain compared to normal predicted values. Conclusion: Mechanical neck pain causes decrease in PEF in smartphone addicted population.