1) to examine the effectiveness of group-CBT for patients with severe health anxiety compared to a wait-list group receiving usual care, 2) to perform a categorical and dimensional assessment of personality, 3) to examine predictors of outcome especially comorbid personality disorders, 4) to examine the relation between personality, illness perception and treatment outcome, 5) to compare the cost-effectiveness of these two treatments, 6) at a 2 years follow up to examine the course and long-term effectiveness of group-CBT for patients with severe health anxiety and some also followed by psychological treatment for comorbid personality disorders.