Background: The European Resuscitation Council Guidelines recognise that there is a lack of direct evidence for the effect of age on outcome following cardiopulmonary resuscitation. Aim: To determine the role that advancing age plays in the decision by clinicians to complete a do not attempt cardiopulmonary resuscitation order based on perceived futility. Design: A questionnaire-based trial. Clinicians were randomly assigned to receive one of two versions of a patient case, varying in age but otherwise identical (90 years vs 60 years). Participants were asked to decide whether a do not attempt cardiopulmonary resuscitation form should be completed based on perceived futility for a single patient case. Rates of do not attempt cardiopulmonary resuscitation order were compared between groups. Participants: Consultant physicians, surgeons and anaesthetists from 12 district general hospitals in England. Results: In total, 291 questionnaires were returned. Overall, clinicians were significantly more likely to complete a do not attempt cardiopulmonary resuscitation form for a 90-year-old patient than a 60-year-old patient, when all other factors are equal (67.7% vs 7.4%, p < 0.001). This finding was consistent across speciality and experience level of the consultant. Surgeons were found to be significantly less likely to complete a do not attempt cardiopulmonary resuscitation order in the 90-year-old patient compared to other consultants (46.4% vs 74.1%, p < 0.001). Anaesthetists were more likely than other consultants to complete a do not attempt cardiopulmonary resuscitation order in the 60-year-old patient (17.8% vs 4.3%, p < 0.05). Conclusion: Age is a highly significant independent factor in a clinicians’ decision to withhold cardiopulmonary resuscitation. We highlight a potential gap between current practice and supporting evidence base.