An 18-year-old Appaloosa gelding was presented for a one-month history of intermittent left unilateral retromandibular swelling, dysphagia, and pyrexia. The swelling decreased with a short course of antibiotics and anti-inflammatories, but never completely resolved. Upon arrival, the patient was bright and vital parameters were within normal limits. Firm, warm, painful soft tissue swellings were palpated along the left mandible and parotid region. The remainder of the physical examination, including a sedated oral examination, was unremarkable. Complete blood count (CBC) demonstrated an inflammatory leukogram with a degenerative left shift. Endoscopically, the larynx, proximal trachea, and right guttural pouch were normal. The left guttural pouch was compressed laterally and ventrally. A lateral radiographic view centered on the larynx revealed severe, locally extensive soft tissue opacities. Ultrasound evaluation demonstrated enlarged left parotid and mandibular glands with multifocal hyperechoic areas and heterogenous fluid in the salivary duct. The surrounding tissue was edematous. These findings were most consistent with unilateral sialoadenitis. This seminar will review sialoadenitis in horses and discuss potential causes, differential diagnosis, and diagnostic and treatment options.