Background: Smartphone use may lead to alterations in spinal kinematics and musculoskeletal discomfort. Objectives: The aim of this study was to evaluate the effect of smartphone use on spinal kinematics, and to examine the relationship between smartphone addiction, spinal discomfort, and gait parameters. Design: Cross-Sectional Study. Methods: The study included 42 healthy adults aged 18–30 years. A photographic method was used for spinal kinematic evaluation in sitting, standing and at the end of a 3-min walk. GAITRite electronic walkway was used for spatiotemporal gait parameters. Smartphone addiction was evaluated with the Smartphone Addiction Scale – Short Version (SAS-SV). The Cornell Musculoskeletal System Discomfort Questionnaire (CMDQ) was used to evaluate feelings of discomfort and pain. Results: There was an increase in head, cervical, and thoracic flexion angles while sitting, standing, and at the end of a 3-min walk. Similarly, an increase in thoracolumbar and lumbar flexion angles was observed only in the sitting position (p < 0.05). While using a smartphone during walking, cadence, walking speed, step length decreased, while step duration and double support duration increased (p < 0.05). A statistically significant correlation was determined between the SAS-SV and CMDQ scores (p < 0.05). Conclusion: The study showed that smartphone use has an impact on spinal kinematics during sitting, standing and at the end of a 3 min-walk, as well as on the spatiotemporal parameters of gait. This study suggest that smartphone addiction should be taken into consideration due to its potential to cause musculoskeletal discomfort and there may be a need to raise public awareness on this matter.