To elucidate the relationship between cerebrospinal fluid (CSF) total‐tau (T‐tau) and phosphorylated tau (P‐tau) with the tau PET ligand 18F‐AV‐1451 in Alzheimer's disease (AD), we examined 30 cognitively healthy elderly (15 with preclinical AD), 14 prodromal AD, and 39 AD dementia patients. The gene discussed is MAPT; the disease is Alzheimer disease.