BACKGROUND: Transabdominal ultrasonography (US) has made the detection of gallbladder polyps easier, but the differential diagnosis of polyps less than 20 mm remains difficult. Therefore, we evaluated the usefulness of endoscopic ultrasonography (EUS) for the differential diagnosis of gallbladder polyps. METHODS: Among patients with gallbladder polyps less than 20 mm, we reviewed 89 patients who underwent US and EUS before surgery and assessed the results of differential diagnoses by them. RESULTS: In all, 86.5% of these polyps were precisely diagnosed by EUS. However, only 51.7% were diagnosed by US. Sensitivity, specificity, and positive and negative predictive values of EUS at the diagnosis of carcinoma were 91.7%, 87.7%, 75.9%, and 96.6%, respectively. Those of US were 54.2%, 53.8%, 54.2%, and 94.6%, respectively. CONCLUSIONS: EUS may markedly improve the accuracy of the differential diagnosis of gallbladder polyps. Therefore, EUS is thought to play an important role in determining the treatment strategy for gallbladder polyps.