An 87-year-old man showed behavioral disinhibition and nocturnal restlessness as well as short-term memory problems. We diagnosed late-onset frontotemporal dementia (LO-FTD), a relatively rare disease. Based on the course of the disease progress, we ruled out medication-induced mania and bipolar disorder. Given the results of the CT-scan, we also dismissed the possibility that the patient was suffering from dementia based on Alzheimer's disease and vascular factors that followed an atypical course. Our article illustrates the complexity of the diagnostic process investigating LO-FTD.