Psychiatric manifestations are infrequent or rarely described in Hashimoto's encephalopathy. It usually begins like a subacute diffuse encephalopathy with confusion, tremor and other neurologic symptoms. A relapsing course is characteristic. Neither biologic nor clinical symptoms are specific but high antithyroid antibodies levels are characteristic. The diagnosis can be seriously delayed by the fact that the different symptoms implicate approaches by psychiatrists, neurologists or endocrinologists. There are two clinical types. The one presented here evaluates progressively to dementia with psychotic episodes, confusion and seizures. An early steroid treatment makes the symptoms regress without aftereffects. We have analysed the clinical and biological findings of a woman who has been admitted to different neurologic and psychiatric departments before her diagnosis was made. First clinical presentation and evolution were that of a depression. Each time the antidepressive treatment was stopped, depression relapsed in spite of an appropriate steroid treatment. Literature shows that a close link exists between depression and antithyroid antibodies whatever thyroid status. This link does still exist after adjustment of psycho-social determinants of depression. The decrease of those antibodies only reflects the decrease of inflammation. So, for the psychiatrist it is important to diagnose Hashimoto's encephalopathy without delay, especially when psychiatric manifestations are in the foreground. Furthermore, a psychiatric report should systematically be added to the clinical and biological findings in order to make a better approach of the existing links between depression and other manifestations of the disease.