The development of accurate diagnostic tests and treatment of dementia must be important issues in an aging society. The quality of biomarkers for dementia have dramatically improved recently and are classified into two categories, including (i) biochemical markers in biofluids and (ii) imaging using radiological technologies. Positron emission tomography (PET) to detect amyloid β was first developed in 2004 (1)). Since then, several amyloid PET tracers to detect senile plaques in patients with Alzheimer's disease (AD) have been published by many investigators, including our group (2)). Some laboratories recently developed PET tracers to detect tau pathologies in patients with AD (3)). Moreover, four drugs (donepezil, galantamine, rivastigmine, and memantin), which modulate neurotransmission in the brains of patients with AD are now used to treat AD; however, none of them can cure the disease. Although several anti-amyloid β compounds have been examined in clinical trials as potentially useful drugs, all of them have failed to show significant benefits so far. In contrast, tau-targeted drugs have been developed and have entered clinical trials. We expect strongly a therapeutic drug for dementia to be released in the near future.