BACKGROUND: Constipation is common in people with advanced cancer and is associated with significant morbidity and health economic burden, but it is often sub-optimally managed. Despite international consensus diagnostic criteria for functional and opioid-induced constipation (Rome IV diagnostic criteria), the term 'constipation' means different things to different people, impacting assessment, diagnosis and management. AIM: To investigate the association between persons with advanced cancer self-reporting of constipation, response to the Rome IV diagnostic criteria statements for opioid-induced constipation and differences according to personal demographics. DESIGN: Multicentre prospective observational study. SETTING/PARTICIPANTS: Twenty-four community, hospice and hospital research sites in 10 European countries recruited 1200 adults with cancer taking opioids for cancer/cancer-treatment related pain. RESULTS: In response to the simple question CONCLUSIONS: There is disparity between patients' self-reporting of constipation and the Rome IV diagnostic criteria. People with advanced cancer, especially those receiving opioid analgesics, need to be regularly assessed for constipation, but the use of a single question (