Objectives: Patellofemoral pain (PFP) is one of the most confusing and clinically challenging chronic diseases. The aim of this study was to determine the validity and reliability of the smartphone goniometer application in patients with PFP by comparing it with a universal and digital inclinometer. Materials and Methods: Twenty-seven patients with PFP were included in this study. Flexion range of motion for the knee joint and flexion/extension, abduction, and internal/external rotation range of motion for the hip joint were measured by two examiners using a smartphone application, a digital inclinometer, and a universal goniometer. To assess inter-rater reliability, the two measurements made by the first observer were evaluated at 24-48 hour intervals. To assess intra-rater reliability, the measurements of both observers were compared. Results: With all three methods, active knee and hip range of motion measurements in PSS patients showed high intra-rater and inter-rater reliability (ICC = 0.69-0.97). Concurrent validity analysis also showed statistically significant, moderate to strong correlations between the three methods (r = 0.562-0.993). SEM and MDC were highest in the goniometer measurement and were intra-observer (3.77-7.94° and 10.44-21.99°, respectively) and inter-observer (2.61-9.45° and 7.23-27.54°, respectively). Conclusion: The smartphone app, inclinometer, and universal goniometer are valid and reliable for measuring lower limb ROM in PFA patients. They can be used in the clinic.