OBJECTIVES: To assess the tolerability and survival outcome of curative radiotherapy in patients over the age of 85 years. DESIGN, SETTING, AND PARTICIPANTS: Retrospective analysis of all patients aged over 85 years who received radiotherapy as part of curative treatment for any cancer (excluding insignificant skin cancers) at the Peter MacCallum Cancer Centre between 1 January 2000 and 1 January 2010. MAIN OUTCOME MEASURES: Poor treatment tolerability (defined as hospital admission during radiotherapy, treatment break, or early treatment cessation); predictors for poor treatment tolerability, overall survival and cancer-specific survival. RESULTS: 327 treatment courses met eligibility criteria. The median age of patients was 87 years. The most common treatment sites were pelvis (30%), head and neck (25%), and breast (18%). The Eastern Cooperative Oncology Group performance status (ECOG PS) score was 0 or 1 for 70% of patients. Overall, 79% of patients completed the prescribed treatment without poor treatment tolerability, and 95% of patients completed all treatment. Only unfavourable ECOG PS score (odds ratio [OR], 1.80; P = 0.005) and increasing age (OR, 1.18; P = 0.018) predicted poor treatment tolerability. ECOG PS score predicted overall survival (hazard ratio, 1.53; P = 0.001). CONCLUSION: Age should not be the sole discriminator in decisions to prescribe aggressive loco-regional radiotherapy. ECOG PS score predicts for treatment tolerability, and also overall survival. The risk of cancer death was higher than non-cancer death for more than 5 years after treatment.