The direct detection of 5-MeV protons by flexible organic detectors based on thin films is here demonstrated. The organic devices act as a solid-state detector, in which the energy released by the protons within the active layer of the sensor is converted into an electrical current. These sensors can quantitatively and reliably measure the dose of protons impinging on the sensor both in real time and in integration mode. This study shows how to detect and exploit the energy absorbed both by the organic semiconducting layer and by the plastic substrate, allowing to extrapolate information on the present and past irradiation of the detector. The measured sensitivity, = (5.15 ± 0.13) pC Gy, and limit of detection, LOD = (30 ± 6) cGy s, of the here proposed detectors assess their efficacy and their potential as proton dosimeters in several fields of application, such as in medical proton therapy.