OBJECTIVE: The major purpose of this study was to compare the frequency of the occurrence of DSM-III diagnoses in patients with primary fibromyalgia syndrome, patients with rheumatoid arthritis, and subjects without pain. METHOD: Thirty-five patients with primary fibromyalgia, 33 patients with rheumatoid arthritis, and 31 nonpatients without pain were blindly assessed for psychiatric diagnoses with the Psychiatric Diagnostic Interview. RESULTS: Data from this interview revealed no group differences in terms of lifetime history of any psychiatric disorders, including major depression, somatization disorder, or anxiety-based disorders. Analysis of the auxiliary symptoms of depression on the Psychiatric Diagnostic Interview revealed that the patients with fibromyalgia did not report a higher frequency of vegetative signs of depression. However, analysis of the somatization scale revealed an interaction between medical and psychiatric diagnoses: patients with primary fibromyalgia syndrome and a psychiatric history endorsed significantly more somatic symptoms than did patients with rheumatoid arthritis or subjects without pain, and fibromyalgia patients without a psychiatric history were no more likely to endorse somatic symptoms than were arthritis patients or subjects without pain. CONCLUSIONS: The Psychiatric Diagnostic Interview data failed to discriminate in any major way between primary fibromyalgia syndrome (a disorder with no known organic etiology) and rheumatoid arthritis (a disorder with a known organic etiology). Therefore, these data do not support a psychopathology model as a primary explanation of the symptoms of primary fibromyalgia syndrome.Abstract Teaser