BACKGROUND: The population prevalence, clinical characteristics, and associations for Rome IV functional dyspepsia are not known. Following the publication of the Rome IV criteria for functional gastrointestinal disorders, we aimed to assess the prevalence, characteristics, and associations for symptom-based Rome IV functional dyspepsia in adults across the USA, Canada, and the UK. METHODS: We sent an internet-based cross-sectional health survey to adults in the general population of three English-speaking countries: the USA, Canada, and the UK. We used quota-based sampling to generate demographically balanced and population-representative samples. Individuals were invited to complete an online questionnaire on general health, without mention that the purpose of this survey was to examine gastrointestinal symptoms. We excluded participants who failed two attention-test questions or were excessively inconsistent on the three gastrointestinal questions that were presented twice in the survey for this particular purpose. The survey enquired about demographics, health-care visits, medications, somatisation, quality of life, and symptom-based criteria for Rome IV functional dyspepsia as well as for irritable bowel syndrome (IBS) and functional heartburn. We made subsequent comparisons between participants with Rome IV functional dyspepsia and controls without dyspepsia. The primary objective was to identify participants who fulfilled symptom-based criteria for Rome IV functional dyspepsia and categorise them into postprandial distress syndrome, epigastric pain syndrome, or overlapping subtypes. FINDINGS: 6300 general population adults completed the health survey; 2100 each from the USA, Canada, and the UK. 369 responses were deemed inconsistent, leaving data for 5931 adults. Rome IV functional dyspepsia was significantly more prevalent in the USA (232 [12%] of 1949) than in Canada (167 [8%] of 1988) and the UK (152 [8%] of 1994; p<0·0001). The subtype distribution was 61% postprandial distress syndrome, 18% epigastric pain syndrome, and 21% overlapping variant with both syndromes; this pattern was similar across the countries. Participants with functional dyspepsia had significantly greater health impairment and health-care usage than those without dyspepsia. Participants with the overlapping variant showed greater somatisation and poorer quality-of-life scores than did individuals with either postprandial distress syndrome or epigastric pain syndrome alone. In multivariate analysis, independent factors associated with all functional dyspepsia subtypes included worsening quality of life and the presence of symptoms compatible with functional heartburn and IBS, with functional heartburn and IBS having the strongest association with overlapping postprandial distress syndrome and epigastric pain syndrome. Notably, somatisation showed a positive association with postprandial distress syndrome and the overlapping variant, and use of antidepressants showed a negative association with postprandial distress syndrome. INTERPRETATION: Approximately 10% of the adult population fulfils symptom-based criteria for Rome IV functional dyspepsia and incurs considerable associated health impairment. The functional dyspepsia subtypes show differing associations, suggesting differences in pathophysiological processes or influences. FUNDING: The Rome Foundation, the US National Institute of Diabetes and Digestive and Kidney Diseases, the Swedish Medical Research Council, AFA Insurance, Ferring Pharmaceuticals, and the Faculty of Medicine, University of Gothenburg, Gothenburg, Sweden.