Several studies have underlined the high prevalence of psychiatric symptoms and disorders in thyroid diseases. The aim of this study was to evaluate the prevalence of psychiatric disorders in 93 inpatients affected by different thyroid diseases during their lifetimes, by means of a standardized instrument, i.e., the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders-III-Revised, Upjohn Version (SCID-UP-R). The results showed higher rates of panic disorder, simple phobia, obsessive-compulsive disorder, major depressive disorder, bipolar disorder and cyclothymia in thyroid patients than in the general population. These findings would suggest that the co-occurrence of psychiatric and thyroid diseases may be the result of common biochemical abnormalities.