Dementia is defined as significant acquired cognitive impairment in one or more cognitive domains that represents a significant decline from previous baseline and interferes with independence in daily activities. Autoimmune dementia is a term that has been used to describe a steroid-responsive autoimmune disorder characterized by a rapidly progressive dementia with a fluctuating course. Even compelling evidence suggests that the immune system plays a critical role in the pathophysiology of Alzheimer disease, the most common type of neurodegenerative dementia. According to literature, autoimmune dementia can be due to these disorders: Paraneoplastic and autoimmune limbic encephalitis, encephalopathy associated with systemic autoimmune, and multiple sclerosis. Paraneoplastic limbic encephalitis is characterized by acute or subacute mood and behavioral changes, short-term memory problems, complex-partial seizures, and cognitive dysfunction. The subacute memory loss is a hallmark of the disorder but it can be overlooked easily because of the presence of other symptoms. Hashimoto's encephalitis or encephalopathy (HE) is a rare autoimmune disease often under diagnosed. It can present as rapidly progressive dementia which is treatable with high dose steroids. Early diagnosis and prompt initiation of steroid therapy are associated with good prognosis. Progressive cognitive impairment has been also described in association with systemic lupus erythematosis, Sjogren syndrome, and Behcet disease. These conditions typically produce nonvasculitic encephalitis. In summary, a high clinical suspicious is essential to make an appropriate diagnosis of autoimmune dementia.