Background: Elderly patients are often excluded from advanced treatments owing to clinical complexity or frailty. Magnetic resonance–guided radiotherapy (MRgRT) represents a new frontier of radiotherapy delivery that can play an important role in the management of these patients. Aim: To assess MRgRT feasibility in elderly patients, describe their compliance with this treatment, and provide a scoring system for elderly patient selection. Methods: Patients aged >75 years were enrolled. No restrictions on tumor site, staging, or treatment intent were applied. Patients underwent joint radiation oncology–geriatrics visits to assess the feasibility of MRgRT and to identify the most significant items (i.e. clinical variables) for the setup of a scoring system. The proposed scoring system was then internally validated on a prospectively enrolled cohort of elderly patients who were candidates for MRgRT. Results: Thirty patients were enrolled between February and March 2018. Their mean age was 81.4 ± 3.4 years (range 75–88). Radiotherapy intent was curative in 26 patients; 14 patients were considered frail at screening tests before radiotherapy. Twelve items were identified as clinically significant for the setup of the MASTER score (MRI-Guided Radiotherapy Selection Elderly Score) score. Validation of the score showed 100% reliability, with no patient discharged after selection. Conclusions: MRgRT appears to be feasible in elderly patients and the MASTER score is proposed to support clinical decision-making in recommending elderly patients for this technology.