QT dispersion is defined as the difference in QT interval between the different leads of the surface 12-lead ECG. This may provide an indirect measure of the underlying inhomogeneity of myocardial repolarization, which is believed to be important in arrhythmogenesis. Methodology for determining QT dispersion varies significantly between studies, and the results of these studies need to be interpreted in light of the methodology used. Although QT dispersion is developing into an important research tool, as yet it has no established role in clinical practice. Once standardization of methodology is achieved a clinical role may emerge, particularly in the assessment of patients before and after intervention aimed at reduction of arrhythmia risk.