Primary intraosseous carcinoma (PIOC) or Primary intraosseous squamous cell carcinoma (PIOSCC) is a rare carcinoma, which arises within the jaws without connection to the oral mucosa. It was first described by Loos in 1913 as a central epidermoid carcinoma of the jaw. The etiology of this tumor is still not clear. It is a rare case which arises by direct transformation of Odontogenic epithelial rests in the jawbone. The epithelial rests found within the periodontal ligament and alveolar bone. Remnants of the dental lamina and the reduced enamel epithelium surrounding anunerupted/impacted tooth, The present report describes a case of PIOC of mandible arising de novo in a 51-year-old-man, which was initially treated by a general dentist, who misdiagnosed it as a periodontal lesion.