A systematic review of the epidemiology of gastro-oesophageal reflux disease (GORD) has been performed, applying strict criteria for quality of studies and the disease definition used. The prevalence and incidence of GORD was estimated from 15 studies which defined GORD as at least weekly heartburn and/or acid regurgitation and met criteria concerning sample size, response rate, and recall period. Data on factors associated with GORD were also evaluated. An approximate prevalence of 10-20% was identified for GORD, defined by at least weekly heartburn and/or acid regurgitation in the Western world while in Asia this was lower, at less than 5%. The incidence in the Western world was approximately 5 per 1000 person years. A number of potential risk factors (for example, an immediate family history and obesity) and comorbidities (for example, respiratory diseases and chest pain) associated with GORD were identified. Data reported in this systematic review can be interpreted with confidence as reflecting the epidemiology of "true" GORD. The disease is more common in the Western world than in Asia, and the low rate of incidence relative to prevalence reflects its chronicity. The small number of studies eligible for inclusion in this review highlights the need for global consensus on a symptom based definition of GORD.