BACKGROUND: The Rome IV criteria for disorders of gut-brain interaction define irritable bowel syndrome (IBS) as a functional bowel disorder associated with frequent abdominal pain of at least 1 day per week. In contrast, functional diarrhea (FD) and functional constipation (FC) are relatively painless. We compared differences in mood and somatization between Rome IV IBS and FC/FD. METHODS: A total of 567 patients with Rome IV defined IBS or FD/FC completed a baseline questionnaire on demographics, abdominal pain frequency, mood (hospital anxiety and depression scale, HADS), and somatization (patient health questionnaire, PHQ-12). The primary analysis compared differences in mood and somatization between IBS and FC/FD, and the relative influence of abdominal pain frequency on these extra-intestinal symptoms. The secondary analysis evaluated differences across individual IBS subtypes, and also between FC and FD. KEY RESULTS: Patients with IBS-in comparison to those with FC/FD-had significantly higher mean PHQ-12 somatization scores (9.1 vs. 5.4), more somatic symptoms (6.0 vs. 4.3), abnormally high somatization levels (16% vs. 3%), higher HADS score (15.0 vs. 11.7), and clinically abnormal levels of anxiety (38% vs. 20%) and depression (17% vs. 10%). Increasing abdominal pain frequency correlated positively with PHQ-12, number of somatic symptoms, and HADS; p < 0.001. No differences in mood and somatization scores were seen between individual IBS subtypes, and nor between FC and FD. CONCLUSION & INFERENCES: Based on the Rome IV criteria, IBS is associated with increased levels of psychological distress and somatization compared with FD or FC. Patients reporting frequent abdominal pain should be comprehensively screened for psychosomatic disorders, with psychological therapies considered early in the disease course.