Abstract Aim To evaluate the accuracy of preoperative diagnosis of acute cholecystitis (AC). Methods A prospective database of cholecystectomies and bile duct explorations spanning 30 years was analysed. Results 593/6140 patients (9.6%) had a preoperative diagnosis of AC (Group 1) 12.3% had no AC at surgery. 300/5547 patients (5.4%) had AC without preoperative criteria (Group 2).Group 1Group 2Emergency admission588 (99.1)203 (67.6)Presentation with Jaundice96 (16.2)110 (36.6)Previous acute cholecystitis76 (12.8)3 (1)USS:GB Thick wall or contraction389 (65.6)112 (37.3))Bile duct dilatation66 (11.1)179 (36.6)Preoperative imaging:MRCP23 (3.8)21 (7)CT76 (12.8)15 (5)ERCP8 (1.35)11 (3.6)Operative GB findingsAcute193 (32.5)140 (46.7)Empyema313 (52.8)160 (53.3)Difficulty Grading I&II20 (3.4)--III177 (29.8)117 (39.1)IV344 (58)168 (56.2)V52 (8.8)15 (4.7)Adhesions GB to:Duodenum503 (84.8)241 (80.3))Hepatic flexure410 (69.1)169 (56.3)Difficult cystic pedicle524 (88.3)273 (91)Fundus first dissection39 (6.6)19 (6.3)Bile Duct Exploration:106 (17.8)98 (32.6)Transcystic93 (15.6)72 (24)Choledochotomy13 (2.2)26 (8.7)Operative time (median, range)80 min (32-280)85 (35-350)Open conversion3 (0.5)3 (1)Morbidity40 (6.7)30 (10)Hospital stay (median, range)9.9 (1-62)13 (1-100)Mortality4 (0.67)1 (0.3)Resolved in one episode427 (72)189 (63) Conclusions 300/806 (37.2%) of AC or empyema encountered at operation do not have preoperative criteria. 25% of all AC require bile duct exploration. Emergency biliary admissions should be dealt with by specialist surgeons.