Musical hallucinations are a well known although rare phenomenon in neurological and psychiatric patients. Many case reports have been published to date. However, an accepted common theory on the classification and on the pathophysiology of musical hallucinations is still missing. We analysed all cases published to date, including two own cases, with respect to their demographic and clinical features and to the possible pathomechanisms underlying the hallucinations. In total, 132 cases could be analysed statistically and separated into five groups according to their aetiology (hypacusis; psychiatric disorder; focal brain lesion; epilepsy; intoxication). There was a female preponderance of 70% and a mean age of 61.5 years. Patients with focal brain lesions were significantly younger than the other groups, the hemisphere of the lesion did not play a major role. No systematic studies on treatment are available. However, anticonvulsant and antidepressive substances were reported to be effective most consistently. The pathophysiology of musical hallucinations is discussed considering the theories of deafferentiation including the concept of auditory Charles-Bonnet syndrome, of sensory auditory deprivation, of parasitic memory, and of spontaneous activity in a cognitive network module. In conclusion, musical hallucinations are a phenomenon with heterogeneous clinical and pathophysiological backgrounds.