Inflammatory bowel disease is a group of chronic medical conditions comprising Crohn’s disease and ulcerative colitis that involves increased frequency of mental disorders. The most common psychiatric disorders in inflammatory bowel disease are depression and anxiety, however, some epidemiologic and biological evidence suggest that other disorders like bipolar disorder occur more often. Biological mechanisms concerning both inflammatory bowel disease and depression or anxiety explain susceptibility to developing mental disorders in inflammatory bowel disease. Interactions of brain gut-axis, immunological disturbances, oxidative stress and vagus nerve dysfunction play a role in pathophysiology of inflammatory bowel disease and mental disorders as well. Significance of these factors was covered in this paper. Psychiatric comorbidity in IBD may affect course of intestinal disease. It can increase requency and severity of relapses and hinder the treatment so knowledge about relationship between IBD and mental health appears to be vital for proper management of patients with inflammatory bowel disease.