[Reversible dementia].

A 65 year old woman, referred for differential diagnosis of dementia, presented with cognitive and mnestic deficits. Typical signs and symptoms of hypothyroidism led to the diagnosis of severe autoimmune thyroiditis. After six months of treatment with thyroid hormone, dementia, myopathy and ataxia had disappeared. The neurologic and neuropsychologic manifestations of hypothyroidism are discussed. In dementia the diagnosis of secondary and reversible forms is of great importance with regard to prognosis and treatment. Hypothyroidism is known to be a common and treatable cause of pseudodementia. Early diagnosis and adequate treatment are important to prevent further permanent deterioration of cerebral function.