The prevalence of severe health anxiety is reported to be 1-2% in Western communities. This functional disorder is difficult for medical doctors to treat, the course of the disorder is often chronic, and that is costly for the social and health care systems as well as for the patients. A Cochrane metaanalysis from 2009 finds evidence for effectiveness of individual cognitive behavior therapy (CBT) for patients with hypochondriasis. But no randomised controlled trials (RCT) of the effectiveness of classical CBT delivered only in groups for patients with severe health anxiety (hypochondriasis/illness anxiety disorder) has yet been conducted.