Infectious or inflammatory conditions can cause inflammation of the gingiva and oral mucosa. Unfortunately, the termstomatitishas historically been and continues to be used loosely, blurring the discussion and treatment of inflammatory conditions in the feline oral cavity; the true definition of stomatitis is inflammation of the oral cavity.4Biopsy and histopathology findings of the oral cavity are often reported as variants of lymphoplasmacytic gingivitis, mucositis, or stomatitis, which implies chronic inflammation. The more common age-related periodontal disease and aggressive periodontitis, caused by subgingival plaque biofilms, should not be mistaken for the less common, true immune-dysregulated stomatitis (Figure 9).13,14 True immune-dysregulated stomatitis has a component of caudal mucositis. Corticosteroids and antibiotics are inappropriate for the treatment of periodontal bacterial-induced oral inflammation. General anesthesia, oral examination with periodontal probing, and full-mouth intraoral radiographs are necessary to differentiate periodontally inflamed tissue from true immune-dysregulated oral mucosa. Short- and long-term surgical and medical treatment plans are based on accurate diagnosis. Although stomatitis is often discussed in relation to feline patients, there are painful stomatitis conditions that also occur in the dog.