ObjectivesAnalyze the characteristics of patients undergoing interventional sialendoscopy for sialolithiasis whose stones were not visualized intraoperatively.Study DesignCase series with chart review.SettingTertiary care hospital.Subjects and MethodsPatients (n = 276) undergoing sialendoscopy between June 2008 and December 2014 were reviewed for patient characteristics, imaging characteristics, and outcomes. Nonvisualization was defined as a sialolith that was documented on imaging preoperatively but not visualized intraoperatively during sialendoscopy, despite successful ductal cannulation and evaluation.ResultsA total of 337 sialendoscopy procedures were preformed. Preoperative imaging documented a sialolith in 203 (60%) cases. Nonvisualization occurred in 31 (15%) cases with sialolith. The parotid gland was involved in 58% (18 of 31) of nonvisualization cases, as opposed to 21% (43 of 203) of all sialolith cases. The submandibular gland was involved in 42% (13 of 31) of nonvisualization cases, as compared with 79% (160 of 203) of all sialolith cases. Nonvisualization occurred in 42% (18 of 43) of parotid cases versus 8% (13 of 160) of submandibular cases, a statistically significant difference (P <. 001). Parotid stones located posterior to the plane of insertion of the posterolateral edge of the masseter were significantly more likely to experience nonvisualization (73%) than those along and anterior to the masseter (25% and 0%, respectively; P =. 009).ConclusionsIntraoperative nonvisualization of a sialolith is more likely to occur in the parotid gland. Proximal stone location may predict nonvisualization. These factors should be considered during treatment planning and counseling for patients with sialolithiasis.