In the upper and lower jaws there can be some anatomical or histological specificities of the denture-bearing areas. Therefore, it is sometimes impossible to take an adequate anatomical impression showing all the tissue of the denture-bearing area or a functional impression which will provide a valve effect, good retention and good stabilization of the dentures. During impression taking of the upper jaw dentist should be aware of the undermining alveolar ridge and maxillary tuberosity, maxillary torus that crosses the ''A line'', highly fibrous tissue in the area of the pterygomandibular raphe, low frenulum labii superioris, low plicae buccales premolares, buccal exostoses, flabby ridge and should know how to recognize and treat chronic inflammation of palate tissue caused by the upper dentures (stomatitis prosthetica). The structures of the lower jaws that can cause problems are mandibular torus, sharp mandibular ridge, buccal exostosis and sharp linea mylohyoidea in the back of the sublingual space in a patient with atrophic alveolar ridge. All of the above-mentioned forms of the upper and lower denture-bearing areas need to be recognized and treated or special impression techniques should be used to achieve the retention and stability of dentures in the denture making process. The first clinical stage of the development of complete dentures is an anatomical impression. It is a negative likeness of the denture-bearing tissues. Based on the cast of the anatomical impression, a special tray is constructed and used to take a functional impression. The functional impression is the most important phase. It shows the shape of the denture-bearing area and forms the functional margins of a future denture. If the tissue specificities are not recognized in a timely manner, the anatomical impression will not show all the denture-bearing area, nor will stabilization, retention and valve effect be accomplished with the functional impression.