Odontogenic cysts are derived from odontogenic epithelium, can be locally invasive and destructive and have been reported rarely in cats. A 16-year-old, male domestic shorthair cat had a 3-year history of a slowly progressive, right mandibular swelling. Intraoral dental radiographs revealed a multilocular, radiolucent, cystic mass within the right mandible that extended from the distal aspect of the canine tooth to the mesial aspect of the fourth premolar tooth. Radiographically, the mass was associated with distortion and regional destruction of the right mandibular bone and resorption of regional tooth roots. Histological examination of an incisional biopsy sample revealed multiple ruptured cysts lined by stratified squamous epithelium of odontogenic origin with luminal parakeratinization and a prominent palisading basal cell layer. The cyst contained abundant orthokeratotic and parakeratotic keratin. The clinical, radiographical and histological features were consistent with a diagnosis of odontogenic keratocyst, as seen in man. This is the first report of an odontogenic keratocyst in a cat.