Context: Hashimoto's encephalopathy is a rare neurological disorder associated with autoimmune thyroiditis. It occurs primarily in the fifth decade of life. However, different age groups may also develop the disease, with serious consequences if unrecognized and untreated. Clinically, it comprises two forms: a sudden vasculitic, and progressive subacute type with wide neuropsychiatric manifestations including confusion, seizures, short term memory impairment, depressed mood and psychosis. Objective: The objective of this report is to present an unusual case of Hashimoto's encephalopathy presented with the acute confusional state. Case presentation: We report the case of a 30-year-old male medically free presented with acute behavioral changes and confusion. Serological studies revealed elevated thyroid peroxidase antibodies levels. In addition, EEG findings of slow background. He was diagnosed as a case of Hashimoto's encephalopathy and he was improved after initiation of intravenous Methylprednisolone therapy. Conclusion: Hashimoto's encephalopathy can present with a challenging clinical picture that may go unrecognized for a long time. Therefore, one should keep in mind the importance of evaluating thyroid function and thyroid antibodies levels in patients presented with unexplained neurocognitive and psychiatric manifestations.