Medical training teaches physicians to sit when breaking bad news, though there have been no controlled studies to support this advice. We aimed to establish cancer patients' preference for physician posture when physicians break bad news using a randomized controlled crossover trial in a department of palliative care at a large US cancer center. Referred patients were blind to the hypothesis and watched video sequences of a sitting or standing physician breaking bad news to a cancer patient and 168 of 173 participants (88 female) completed the study. Sitting physicians were preferred and viewed as significantly more compassionate than standing physicians (P < 0.0001) but other physician attributes and behaviours were generally rated as of equal or more importance than posture. In summary, cancer patients, especially females, prefer physicians to sit when breaking bad news and rate physicians who adopt this posture as more compassionate. However, sitting posture alone is unlikely to compensate for poor communication skills and lack of other respectful gestures during a consultation.