A 58-year-old female was diagnosed with Alzheimer’s dementia (AD) which was rapidly progressive in the 8 months prior to initiation of hyperbaric oxygen therapy (HBOT). Fluorodeoxyglucose (FDG) positron emission tomography (PET) brain imaging demonstrated global and typical metabolic deficits in AD (posterior temporal-parietal watershed and cingulate areas). An 8-week course of HBOT reversed the patient’s symptomatic decline. Repeat PET imaging demonstrated a corresponding 6.5–38% regional and global increase in brain metabolism, including increased metabolism in the typical AD diagnostic areas of the brain. Continued HBOT in conjunction with standard pharmacotherapy maintained the patient’s symptomatic level of function over an ensuing 22 months. This is the first reported case of simultaneous HBOT-induced symptomatic and FDG PET documented improvement of brain metabolism in AD and suggests an effect on global pathology in AD.