We describe a unique case of a 62-year-old patient with recurrent right submandibular sialadenitis. He initially appeared to have extensive sialolithiasis of the right submandibular duct on computed tomography imaging and examination, but sialendoscopy demonstrated a normal-appearing right submandibular duct. An accessory duct posterior and parallel to the normal duct was identified at the time of sialendoscopy and was found to have extensive sialolithiasis, which required removal by both an endoscopic and intraoral technique. To the best of our knowledge, this is the first report of sialolithiasis of an accessory submandibular duct identified at the time of sialendoscopy; the other few reported cases in the literature are based primarily on findings from traditional sialography or magnetic resonance sialography. Identification of accessory salivary ducts requires intraoperative consideration of this entity during sialendoscopy. Open approaches to sialolithiasis, however, may be aided by appropriate preoperative imaging.