Gallbladder cancer is among the organs examined in mass screening for cancer using ultrasonography; the reported prevalence of gallbladder cancer in such screening of a general population was 0.011%, while the prevalence of gallbladder polyps was reported as 4.3 to 6.9%. Endoscopic ultrasonography is useful for the differential diagnosis of gallbladder tumors detected by mass screening, as well as for estimating the depth of tumor invasion and detecting abnormal connections between pancreatobiliary ducts. While a systematic approach leading to diagnosis by endoscopic ultrasonography is useful, recent advances of contrast-enhanced ultrasonography are expected to establish it as a new modality for early detection. At our hospital, 7 of 26 patients with abnormal connections between pancreatobiliary ducts developed gallbladder carcinoma (23.1%), and 7 of 48 patients with gallbladder carcinoma had abnormal connections between pancreatobiliary ducts (12.5%). Serial observation in patients with gallstones and prophylactic surgery in patients with abnormal connections between pancreatobiliary ducts are necessary.