In patients with the behavioral variant of frontotemporal dementia, the core clinical phenotype of frontotemporal lobar degeneration, various social behaviors such as disinhibition, apathy, lack of empathy, stereotypy, and changes in eating behavior occur from the onset of the disease, and progresses slowly with frontal lobe damage. Because there are no disease-specific biomarkers, the diagnosis of frontotemporal dementia is based on the evaluation of behavioral symptoms, with neuroimaging methods and cognitive tests as assisting methods. Although diagnostic criteria are useful, frontotemporal dementia may be difficult to differentiate from other conditions, including mental illnesses. We need to be careful to avoid overdiagnosis and underdiagnosis.