A cyst is defined as a pathological cavity lined by epithelium. The odontogenic keratocyst is the most aggressive and recurrent of all the odontogenic cysts. It shows characteristics resembling both a cyst and a benign tumor. Most (60%) arise from dental lamina rests or from the basal cells of oral epithelium and are thus primordial in origin odontogenic keratocysts. The remaining (40%) arise from the reduced enamel epithelium of the dental follicle and are thus dentigerous origin odontogenic keratocysts. This lesion occurs in all age groups but is more common during the second and third decades of life and is found at the angle and ramus of the mandible. This paper discusses a case of odontogenic keratocyst affecting the mandible, crossing the midline, with a supernumerary tooth in the anterior region.