Sialolithiasis is the formation of salivary stones, or calculi, within the salivary glands or their ducts. The stones are concretions of calcium salts and organic debris that build up when saliva flow slows or its chemistry changes. They lodge most often in the duct of the submandibular gland under the jaw, causing the gland to swell painfully at mealtimes when saliva surges against the blockage. Small stones may pass spontaneously with hydration, sour stimulation, and massage; larger ones require endoscopic or surgical removal. Recurrence prompts investigation of dehydration, medications that dry the mouth, or duct strictures. It is the commonest cause of painful salivary gland swelling.