Abstract Keratocysts are generally considered to be primordial or laminar in origin. Although such a development probably cannot be excluded in certain circumstances, a development from epithelial hamartias in the oral mucosa seems to be more likely, especially in the third molar region and the ascending ramus o£ the mandible. This new theory is based upon studies of the developing dental lamina in human fetuses as well as in the rhesus monkey, Moreover, the clinical and histologic features of six keratocysts are discussed. The findings in these cysts strengthen the idea that the oral mucosa plays an important role in the origin of many keratocysts. As a result of this study we advocate excision of the overlying mucosa in the area where the cysts adhere to the mucosa.