OBJECTIVE: Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder characterized by chronic, relapsing abdominal pain or discomfort and is associated with disturbed defecation. The pathogenesis of IBS is multifactorial. The aim of this study was to investigate the prevalence of IBS using the Rome III criteria and to assess the effects of mental and lifestyle factors on IBS in a community-dwelling population in Japan. METHODS: The diagnosis of irritable bowel syndrome was based on the Japanese version of the Rome III Questionnaire. The questionnaire was administered to 993 volunteers who participated in the Iwaki Health Promotion Project 2013. Diet was assessed with a validated brief-type self-administered diet history questionnaire. Dietary patterns based on 52 predefined food groups [energy-adjusted food (g/d)] were extracted using a principal component analysis. The Center for Epidemiologic Studies Depression Scale with a cut-off point of 16 was used to assess the prevalence of depression. RESULTS: A total of 61 subjects (6.1%) were classified as having IBS. Three dietary patterns were identified: "Healthy", "Western" and "Alcohol and accompanying" dietary patterns. After adjusting for potential confounders, the "Alcohol and accompanying" dietary pattern and depression were related to the risk of IBS. CONCLUSION: We found that an "Alcohol and accompanying" dietary pattern and depression were related to the risk of IBS in a Japanese community population. However, we could not rule out the possibility of some selection bias. Further studies with longitudinal observations are therefore warranted.