Integrating patient-generated data into clinical research would improve the reliability of results, especially when longitudinal, chronic, home-based monitoring is needed. To this end, we designed, implemented, and tested a system that allows integrating patient-generated data into electronic case report form (eCRF), using a standards based architecture that ensured the fulfillment of the major requirements for digital data in clinical studies. The system was tested in a clinical investigation for the optimization of deep brain stimulation therapy in patients with Parkinson's disease that required both the collection of patient-generated data and of clinical and neurophysiological data. The validation showed that the implemented system was able to provide a reliable solution for including the patient as direct digital data source, ensuring reliability, integrity, security, attributability, and auditability of data.