Abstract One hundred and fifty-six successive patients have been admitted with the clinical diagnosis of acute cholecystitis and have been treated by operation on the next operating list. The diagnosis was correct in 154 and a diagnostic pathway has been determined. The clinical features, investigations, bacteriology and pathology are discussed. There is an increased need for choledochotomy in acute cholecystitis and this bile is more commonly infected than in the elective patient. It is suggested that those with infection can be identified prior to operation and should be treated with antibiotics on admission. The morbidity of operation on patients with uninfected bile is no greater than in those receiving elective surgery, and operative treatment is recommended for both groups of patients.