Symptoms of gastroesophageal reflux disease (GERD) are among the most common encountered in primary practice. Reported symptoms certainly under-represent the true prevalence of this disease in the population, because many patients do not seek care for symptoms of GERD and many physicians do not specifically ask about such symptoms when performing the review of systems. We describe the epidemiology of GERD. We begin by considering the prevalence of GERD as a function of the disease definition used. We then discuss the epidemiology of nonerosive reflux disease. After that, we consider the population risk factors for GERD. Next, we briefly touch on the epidemiology of GERD complications, including erosive esophagitis, strictures, and Barrett esophagus. We will end with a brief discussion of population screening of those with GERD for Barrett esophagus.