Musical hallucinations have been described in numerous neurologic and psychiatric patients, but their pathophysiologic background is not understood. Analyzing the published cases, five subgroups can be separated according to their etiology: hypacusis, psychiatric disorders, focal brain lesions, epilepsy, and intoxication. There is a female preponderance of about 70%. Musical hallucinations most often occur in patients over age 60 years, although patients whose hallucinations are caused by focal brain lesions are significantly younger. Hemispheric dominance seems to play no major role in the pathogenesis of musical hallucinations, but hypacusis is present in the majority of all patients. Anticonvulsant and antidepressive agents have been effective in the treatment of some musical hallucinations. The discussion on the pathophysiology of musical hallucinations comprises theories of deafferentation (including auditory Charles Bonnet syndrome), of sensory auditory deprivation, of parasitic memory, and of spontaneous activity in a cognitive network module.