BACKGROUND AND AIMS: Psychologic stress can affect the pathogenesis of inflammatory bowel disease (IBD), but the precise contribution of psychologic stress to IBD remains unclear. We investigated the association of psychologic stress with disease activity in patients with IBD, especially in terms of mental state and sleep condition. METHODS: This was a multi-center observational study comprising 20 institutions. Data were collected using survey forms for doctors and questionnaires for patients, and the association of psychologic stress with clinical parameters was investigated. Mental state was evaluated using the Center for Epidemiologic Studies Depression (CES-D) scale, and sleep condition was evaluated by querying patients about the severity of insomnia symptoms. RESULTS: A total of 1078 IBD patients were enrolled, including 303 patients with Crohn's disease and 775 patients with ulcerative colitis. Seventy-five percent of IBD patients believed that psychologic stress triggered an exacerbation of their disease (PSTE group) and 25% did not (non-PSTE group). The CES-D scores were significantly higher for patients with clinically active disease than for those in remission in the PSTE group (median (interquartile range) = 7 (4-9.5) vs. 5 (3-7), p < .0001), but not in the non-PSTE group (5 (2-8) vs. 4 (3-7), p = 0.78). Female sex and disease exacerbation by factors other than psychologic stress were independent factors of psychologic stress-triggered disease exacerbation. Also, patients with insomnia had higher disease activity than those without insomnia, especially in the PSTE group. CONCLUSIONS: A worsened mental state correlates with disease activity in IBD patients, especially those who believe that their disease is exacerbated by psychologic stress.