Smartphone-based accelerometers offer a cost-effective and portable alternative to traditional gait analysis systems, with high reliability in measuring key parameters such as walking speed, cadence, and distance. This study assessed their validity compared to the GAITRite system, a widely recognized gold-standard tool, using data from 30 healthy adults walking at 3 self-selected speeds: preferred, slow, and fast. The results demonstrated a high degree of agreement between the two systems, with intraclass correlation coefficients (ICCs) ranging from 0.778 to 0.999. Although the findings emphasize the potential of smartphone accelerometers for clinical and real-world applications, certain limitations were noted, including participant homogeneity and minor discrepancies at extreme walking speeds. To address these limitations, incorporating data from additional sensors, such as gyroscopes and magnetometers, may enhance the accuracy and reliability of spatial parameter estimation. Overall, the findings support the use of smartphone accelerometers as a promising tool for advancing gait monitoring technologies, particularly in the contexts of telerehabilitation and mobility assessments.