Lyme disease is an uncommon cause of reversible dementia. A 75-year-old male patient, with a personal history of mild memory deficit, was admitted to Alzheimer’s Disease Care Unit due to hallucinations, confusion and aggressive behavior unresponsive to antipsychotic therapy. A computed tomography (CT) scan of the brain was negative, while blood exams showed a rise in inflammatory parameters. A complete screening of infective diseases showed a positive serology for Borrelia burgdorferi, confirmed at Western blot. Even though the patient refused cerebrospinal fluid (CSF) exam, the brilliant clinical improvement after the appropriate antimicrobial therapy is strongly suggestive for a diagnosis of neuroborreliosis. This case report underlines the importance of a diagnostic approach to dementia, as to find out and treat the reversible causes.