Non-alcoholic fatty liver disease is increasingly being recognized as an important and common condition, affecting approximately 20% of the general population. Although liver biopsy is currently the gold standard for diagnosis, there is a need for less invasive methods. Imaging by ultrasound, computerized tomography and magnetic resonance are all able to demonstrate fat. In this paper, these three imaging techniques are critically assessed. Ultrasound, although probably not the most reliable imaging method, has many advantages and, when positive, gives a high degree of certainty of the diagnosis depending on the prevalence of fatty liver in the population being studied. Unlike liver biopsy, none of these techniques is able to differentiate simple steatosis from non-alcoholic steatohepatitis.