OBJECTIVES: A histopathological tumor thickness of ≥1000 μm has been reported as one of many risk factors for recurrent lymph node metastasis in superficial pharyngeal cancer (SPC). However, methods for assessing this risk factor preoperatively have not yet been established. Hence, the current study aimed to evaluate the efficacy of endoscopic ultrasonography (EUS) in measuring tumor thickness preoperatively in patients with SPC. METHODS: This single-center retrospective study included 44 consecutive patients with 47 lesions who underwent endoscopic submucosal dissection (ESD). Prior to surgery, EUS examination was performed while under general anesthesia. Further, microvascular irregularity in the target lesion was evaluated using the Japan Esophageal Society (JES) magnification endoscopic classification system. RESULTS: A significant correlation was noted between histopathological and EUS tumor thickness (Spearman's correlation r == 0.879, p < 0.001). In tumors ≥1000 µm thick on histopathology, the cutoff value for EUS tumor thickness was 2.6 mm, and the following values were obtained: sensitivity, 100%; specificity, 81.8%; positive predictive value (PPV), 70%; negative predictive value (NPV), 100%; and accuracy, 87.2%. In B2 lesions ≥1000-μm thick, the following values were obtained: sensitivity, 85.7%; specificity, 90.9%; PPV, 80%; NPV, 93.8%; and accuracy, 89.4%. The diagnostic accuracy rate of combined EUS and the JES magnifying endoscopic classification system was 95.7%. CONCLUSIONS: Tumor thickness assessed using EUS was effective in diagnosing histopathological tumor thickness of ≥1000 μm. The combined use of EUS and the JES magnifying endoscopic classification system may be useful for assessing preoperative risk factors for lymph node metastasis in SPC.