Periodontal disease is the most commonly diagnosed problem in small animal veterinary medicine. In the vast majority of cases, however, there are little to no outward clinical signs of the disease process, and, therefore, therapy often comes very late in the disease course. Consequently, periodontal disease is also the most undertreated animal health problem. In addition, unchecked periodontal disease has numerous dire consequences both locally and systemically. These consequences are detailed in the article and should be utilized to educate clients and encourage compliance of therapeutic recommendations. The local consequences include oronasal fistulas, class II perio-endo lesions, pathologic fractures, ocular problems, osteomyelitis, and an increased incidence of oral cancer. Systemic diseases linked to periodontal disease include: renal, hepatic, pulmonary, and cardiac diseases; osteoporosis, adverse pregnancy effects, and diabetes mellitus. Before the discussion of consequences, this article covers the pathogenesis of periodontal disease, followed by clinical features and diagnostic tests.