The role of acid in the pathogenesis of gastro-oesophageal reflux disease (GERD) has been extensively studied and is well accepted. The role, if any, of non-acid reflux, in particular duodenogastro-oesophageal reflux, is much debated. The availability of new technology to detect non-acid reflux has heightened interest in this question. This article reviews the following: How do we define non-acid reflux? Does duodenogastro-oesophageal reflux (alone or in combination) cause oesophageal injury, symptoms or both? What is its role in complicated GERD? What methods are available to assess non-acid reflux? Does non-acid reflux need treatment and if so what modalities are available?