Illness anxiety disorder (IAD) is a diagnosis introduced by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), in 2013 for individuals with heightened and disabling anxiety about health and few or no somatic symptoms. IAD has replaced hypochondriasis and health anxiety, and most information on IAD comes from research conducted on these disorders. Based on this research, it appears that IAD has important relations with major depressive disorder, panic disorder, obsessive-compulsive disorder (OCD), somatic symptom disorder, and personality disorders and that it is particularly common in primary care and in specialized medical settings. The cause of IAD is not known, but cognitive, information-processing, and behavioral models of health anxiety have contributed to a better understanding of it. A good therapeutic relationship is ...