This course helps you learn about the familiarity with the radiological features on 2D radiographs and on CBCT and the differential diagnoses of well defined unilocular diseases encounter in the jaws. Lesions that commonly present as well-defined radiolucencies are cysts and neoplasms. Cysts are common and the majority are inflammatory. Almost all true cysts and most benign neoplasms expand by hydrostatic pressure and are therefore frequently spherical or nearly spherical in shape. This shape is achieved in larger cysts and neoplasms by displacing the buccal and lingual cortices and presenting as buccolingual expansion. Odontogenic or non odontogenic lesions, arising within the jaws, if sufficiently large will displace the mandibular canal, create resorption of the adjacent teeth and expand the cortices. These lesions may enlarge considerably if allowed to develop unchecked, and have the potential for pathological transformation. In this lecture we will address the radiological appearance of the most common well defined unilocular radiolucencies of the jaws and highlight the importance of early detection and management of such lesions.