Heart failure (HF) is a major public health problem. Clinical studies suggest that a significant proportion of patients with HF have preserved ejection fraction, a clinical syndrome commonly referred to as diastolic HF (DHF). One of the purposes of epidemiological studies is to identify unmet public health needs in a population and to quantify the magnitude of the problem in a manner that is free from the referral bias inherent in clinical studies. We review current epidemiological data estimating the prevalence of DHF, highlight the challenges posed by existing data, and suggest focus for future studies on the epidemiology of DHF. We limited the review to studies that met our definition of population-based studies (eg, studies drawing participants from a defined community or all consecutive referrals to a health facility that is the sole provider to a defined community). Studies relevant to the epidemiology of each stage of DHF (American College of Cardiology/American Heart Association stages A-D) were reviewed. These epidemiological studies clearly define the magnitude of this health care problem and underscore the urgent need for studies elucidating the natural history, pathophysiology, and optimal diagnostic and management strategy for this extremely common clinical syndrome.