Abstract Objective The purpose of this study was to define and select a core set of outcome-based quality indicators, accepted by stakeholders on usability and perceived added value as a quality improvement tool, and to formulate recommendations for the next implementation step. Methods In phase 1, 15 potential quality indicators were defined for patient-reported outcome measures and associated domains, namely the Numeric Pain Rating Scale (NPRS) for pain intensity, the Patient Specific Functioning Scale (PSFS) for physical activity, the Quebec Back Pain Disability Scale for physical functioning, and the Global Perceived Effect—Dutch Version for perceived effect. Their comparability and discriminatory characteristics were described using cohort data. In phase 2, a core set of quality indicators was selected based on consensus among stakeholders in focus group meetings. Results In total, 65,815 completed treatment episodes for patients with nonspecific low back pain were provided by 1009 physical therapists from 219 physical therapist practices. The discriminability between physical therapists of all potential 15 quality indicators was adequate, with intraclass correlation coefficients between 0.08 and 0.30. Stakeholders selected a final core set of 6 quality indicators: 2 process indicators (the routine measurement of NPRS and the PSFS) and 4 outcome indicators (pretreatment and posttreatment change scores for the NPRS, PSFS, Quebec Back Pain Disability Scale, and the minimal clinically important difference of the Global Perceived Effect—Dutch Version). Conclusion This study described and selected a core set of outcome-based quality indicators for physical therapy in patients with nonspecific low back pain. The set was accepted by stakeholders for having added value for daily practice in physical therapy primary care and was found useful for quality improvement initiatives. Further studies need to focus on improvement of using the core set of outcome-based quality indicators as a quality monitoring and ...