Musical hallucinations are poorly understood auditory hallucinations that occur in patients with otologic or neurologic diseases. We report the first cases of musical hallucinations in two patients with neurologic Lyme disease. Both subjects were women with clinical and laboratory evidence of chronic Lyme disease, progressive neurologic dysfunction, and abnormal magnetic resonance imaging of the brain. There was no evidence of hearing loss in either case. Musical hallucinations had a sudden onset and took the form of patriotic or operatic music. The auditory hallucinations disappeared with intravenous (i.v.) antibiotic therapy in both patients, but the hallucinations recurred when i.v. antibiotic therapy was discontinued in one case. Response to therapy was accompanied by an increase in the CD57 lymphocyte subset in one patient, whereas recurrent hallucinations were associated with persistently low CD57 levels in the other case. We conclude that musical hallucinations may be associated with neurologic Lyme disease. These auditory hallucinations appear to respond to i.v. antibiotic therapy. Patients with musical hallucinations of unknown cause should be tested for infection with the Lyme disease spirochete.