Gastro-oesophageal reflux disease (GERD) is a condition in which the gastro-oesophageal reflux provokes symptoms or complications. Since the majority of patients with heartburn do not have mucosal breaks, expressions such as ‘endoscopy-negative reflux disease’ (ENRD), ‘non-erosive reflux disease’ (NERD), or even ‘reflux-like dyspepsia’ and ‘functional heartburn’ are frequently employed despite the lack of consensus concerning their exact meaning. Moreover, definition of a disease does not mean that precise diagnostic criteria exist. Diagnostic approaches to GERD differ considerably between primary and secondary care. The primary care physician's role is to decide, on the basis of symptoms and clinical examination, if it is likely that the patient has some serious problem which requires urgent investigation and intervention. In practice, a symptom-based diagnosis can often be made reliably because heartburn and regurgitation are very specific for GERD. The secondary care physician has to make a full evaluation of an already highly-selected patient and, as far as possible, to make a comprehensive, accurate diagnosis, using whatever investigative tools are required. However, there is no ‘gold standard’ for the diagnosis of GERD and 24-hour pH monitoring lacks sensitivity in NERD. Recently, impedance-pH monitoring has been introduced and promising results have been reported. However, this new technology needs further validation and technical improvement before being employed in routine clinical investigation.