A variety of tests are available to arrive at the proper diagnosis of oral and perioral diseases, which may be extremely important if further treatment is indicated. When oral cancer is suspected the main diagnostic tool remains the histopathologic examination of a biopsy specimen. The value of cytologic examination, whether obtained by exfoliation of cells or by a brush technique, is somewhat questionable. A positive result of such examination needs to be confirmed by a biopsy. The same applies to the use of toluidine blue stain. The presence or absence and, if present, the degree of epithelial dysplasia as observed in a biopsy is still the most reliable predictor of possible future malignant transformation of oral leukoplakie in spite of recently reported, promising results with DNA-ploidy measurements. A salivary gland biopsy, whether taken from the parotid gland or from the accessory gland of the lower lip, plays a valuable role in establishing a diagnosis of Sjögren’s syndrome. Computertomography (CT) and Magnetic Resonance Imaging (MRI) have become important imaging tools in disease processes in the bones and the soft tissues.