The present thesis deal with the diagnostic boundaries between hypochondriasis and obsessive compulsive disorder and between hypochondriasis and another somatoform disorder called non-cardiac chest... Show moreThe present thesis deal with the diagnostic boundaries between hypochondriasis and obsessive compulsive disorder and between hypochondriasis and another somatoform disorder called non-cardiac chest pain. These studies showed that hypochondriasis and both other disorders are valid disorders based on diagnosis-specific symptoms. Furthermore, in the thesis the first randomized controlled trial comparing the efficacy of cognitive behavioural therapy, and a double-blind SSRI (paroxetine) and pill-placebo is described. The short term effects (4 months) and the long term (5 years) of both treatments were compared to each other and to the placebo. It can be concluded that both are effective treatments for hypochondriasis compared to the placebo in the short term, but the significant differences between both active treatments in ameliorating hypochondriacal symptoms disappears during the follow-up, although CBT is more effective in ameliorating comorbid depressive and psychoneurotic symptoms during the follow-up period than the placebo. Furthermore, CBT results in less use of additional psychological or medical help during the follow-up. Finally, the psychometric properties of the first clinician-administered semi-structured interview, the hypochondriasis Y-BOCS, were described. This interview seemed reliable and valid addition to the assessment arsenal measuring hypochondriacal symptoms. Show less