Musical hallucination is one of the most complex forms of auditory hallucinations, where subjects perceive complex sound in the form of music, in the absence of an acoustic stimulus. It has been reported in patients with diseases such as psychiatric disorders, organic brain diseases, and epilepsy. However, the most common of these are idiopathic musical hallucinations that occur alongside deafness in the elderly. In recent years, there have been many reports of musical hallucination occurring as a result of mild cognitive impairment and dementia. Musical hallucinations accompanying hearing loss may reflect deterioration of cerebral function. It has been suggested that auditory Charles Bonnet syndrome is a pathophysiological mechanism of musical hallucination. The decrease in auditory stimulation and activation of the auditory network may activate the cerebral network in relation to music. It is also thought that musical hallucination appears from disintegration of the complementary relationship between sensation and memory. Treatment is still the focus of extensive investigation. Some authors have reported that hearing aids, antiepileptic drugs, anticholinergics, and antipsychotics can relieve musical hallucination. It is possible that such treatment may lead to relief of musical hallucination in patients with various background diseases. Population aging in Japan has exceeded 20%, which is the highest in the world; therefore, there may be many undiagnosed patients throughout the country.