A 79-year-old woman attended the Center for Comprehensive Care of Memory Disorders at the Kyorin University Hospital in 2006 due to forgetfulness. Her initial diagnosis was vascular dementia. In 2007, her cognition declined gradually. Then, impaired verbal fluency and stuttering, the symptoms of non-fluent aphasia, were presented. Thereafter, 5 mg/day donepezil hydrochloride was prescribed. She later suffered type II respiratory failure. Needle electromyography revealed denervation of lower motor neurons. This led to the diagnosis of frontotemporal dementia with motor neuron disease. Interestingly, before developing type II respiratory failure, cognitive decline and non-fluent aphasia occurred in this case.