Epithelial dysplasia is an unequivocal neoplastic transformation which can be recognized with routine morphology. It is the morphological expression of one of the early steps of carcinogenesis. Its diagnosis depends upon the recognition of cytological and architectural abnormalities. A dysplastic lesion can, according to the severity of these abnormalities, be subdivided into different degrees. The presence of dysplasia in endoscopic biopsies may indicate a precursor lesion but it may also be a marker of malignancy. New techniques looking for molecular alterations can help to make a more reliable diagnosis of dysplasia.