New cases of major depression disorder and anxiety disorders comorbidity are frequently emerging in primary care settings. There are many reasons why it is important to discover, diagnose, and treat the comorbidity of major depression and anxiety disorders. One of the reasons is that anxiety disorders might not be diagnosed or treated if the possibility of comorbidity is not kept in mind. Another reason is that undiagnosed comorbidity of major depression disorder and anxiety disorders might increase the risk of psychiatric hospitalization, physical illnesses, disability, and even suicide. Furthermore, undiagnosed comorbidity of major depression disorder and anxiety disorders might lessen the effect of treatment and create the need for long-term treatment.