Functional dyspepsia is defined as persistent or recurrent upper abdominal pain or discomfort not explained by structural or biochemical abnormalities. In about half of the patients who present to their practitioner with chronic dyspepsia, no underlying disease is established after clinical investigation. Many clinical trials have been performed to demonstrate a certain relationship between functional dyspepsia and several pathogenic mechanisms like dysmotility, Helicobacter pylori infection, acid output and hypersensitivity to distension. Unfortunately, the conclusions of those studies are conflicting. Short-term follow-up, lack of consensus about diagnostic criteria for functional dyspepsia and unvalidated symptom measures make it difficult to interpret their results.