Diabetic macular oedema is a major cause of visual loss in patients with diabetes. It usually results from the breakdown of the inner blood-retinal barrier. Early detection of retinal abnormalities is vital in preventing diabetic macular oedema and subsequent loss of vision, whilst assessment of retinal thickness is important for treatment and follow-up. Until recently, however, the methods available for detecting and evaluating diabetic macular oedema were slit-lamp biomicroscopy and stereoscopic photography, both of which are limited in detecting earlier retinal changes. Optical coherence tomography (OCT) is a new diagnostic imaging modality that provides high-resolution, cross-sectional images of the eye. It is proving to be an accurate tool for the early diagnosis, analysis and monitoring of retinopathy, with high repeatability and resolution. It allows not only the qualitative diagnosis of diabetic macular oedema, but also the quantitative assessment of oedema. This article reviews the future role of OCT in the management of patients with diabetic macular oedema.