To clarify the clinical features of acute acalculous cholecystitis (AAC), we reviewed 113 cases of AAC experienced from January, 2000 to December, 2007 in regard to patient background, etiology, imaging diagnosis, treatment, and outcomes. Functional bile stasis caused AAC in 34 of 113 cases (30.1%), and 28 of those developed in a nosocomial manner (82.4%). On the contrary, mechanical bile stasis caused 37 cases (32.7%), and all but one case developed in a community-acquired manner. mechanical bile stasis included 9 cases of biliary tract neoplasm (5, cystic duct cancer; 3, gallbladder cancer; 1, papillary adenoma). Since considerable cases of AAC were caused by biliary tract neoplasm, we have to pay attention to their existences.