The diagnostic criteria of endoscopic ultrasonography (EUS) in the management of polypoid lesions of the gallbladder was established by a retrospective study using 57 cases with polypoid lesions of the gallbladder that were all resected and confirmed histologically. By this study, EUS findings of polypoid lesions of the gallbladder were classified into the following six groups; Type I with a foamy high echogram, Type II with a globular high echogram, Type III with a papillary high echogram, Type IV with a papillary solid echogram, Type V with a nodular solid echogram and Type VI with a nodular solid echogram including multiple spotty an-echoic areas which suggested the presence of Rokitansky-Aschoff sinus. Comparing the types of EUS findings with histological diagnosis, Type I and II corresponded to cholesterol polyps. Type III and IV contained benign pseudo tumors such as cholesterol polyp or hyperplastic polyp as well as tumorous lesions such as adenocarcinoma or adenoma. Type III with over 10 mm in size and IV with over 5 mm in size had a possibility of tumorous lesions. Type V usually corresponded to adenocarcinoma, and Type VI to adenomyomatous hyperplasia. From these results, the following criteria was established; (1) Polypoid lesions showing Type I, II, III with less than 10 mm in size, IV with less than 5 mm in size and VI should be followed-up as benign diseases. (2) Polypoid lesions of Type III with over 10 mm in size and IV with over 5 mm in size was considered to be relative indications for surgery as tumors. (3) Polypoid lesions of Type V was an absolute surgical indication as malignant. The reliability of this EUS criteria was followingly evaluated by a prospective study using 94 cases with polypoid lesions of the gallbladder; 32 cases with open or laparoscopic cholecystectomy and 62 cases with over one year follow-up observations. The criteria corresponded well with the histological or follow-up findings in Type I, II, III with less than 10 mm in size, IV with less than 5 mm in size, V and VI. It had, however, a tendency of over indications to surgery in Type III with over 10 mm in size and IV with over 5 mm in size because these types were widely set not to overlook tumorous lesions such as adenoma and small adenocarcinoma.(ABSTRACT TRUNCATED AT 400 WORDS)