Fragmented mandibles of two Pleistocene lions (Panthera leo atrox) recovered from Yukon Territory possessed acquired pathological changes and congenital abnormalities, judging from the anatomy of contemporary and modern lions. One specimen showed evidence of chronic periodontitis, an extensive sclerosing osteomyelitis and congenital absence of left lower incisor teeth 1 and 2. The second showed long-standing loss of the left lower canine tooth with subsequent obliteration of the alveolus by lamellar and spicular bone and the congenital absence of two incisors in each half of the mandible. Both specimens had reduced incisive widths.