| GERD and functional dyspepsia are the two most prevalent upper gastrointestinal disorders. Gastro-oesophageal reflux is most commonly diagnosed using the cardinal symptoms of heartburn and regurgitation. Patients might also be diagnosed using a questionnaire, after empiric treatment with an acid suppressant, after upper endoscopy or by pH testing. Functional dyspepsia is best diagnosed using symptoms outlined by the Rome committee in conjunction with a normal upper endoscopy. Theoretically, distinguishing these two populations should be easy for all health-care providers. In reality, however, carefully separating out these two populations can be quite difficult, as substantial overlap exists epidemiologically, symptomatically and even diagnostically. This overlap renders precise diagnosis a challenge; given the limited treatment options, the primary goal is to identify those patients who will respond to acid suppressive therapy. Despite the frequency with which functional dyspepsia and GERD overlap, remarkably few studies have investigated this overlap. Most recommendations are based on data derived from separate studies of functional dyspepsia and GERD. A further limitation of existing studies is their failure to differentiate between the various diagnostic categories into which the individual presenting with heartburn might belong.