CHOLE-POSSUM PRO is a prospective multicenter observational study on patients with ACC candidate to EC. The rationale of the study is to validate the CHOLE-POSSUM PRO SCORE for 30-day mortality in this population.

Inclusion Criteria:

• have a diagnosis of ACC as defined by TG18 criteria
• be ACC candidate to EC during the index admission* (* All the patients treated with initial open cholecystectomy, those who undergo ELC, those with conversion from laparoscopic to open cholecystectomy or those who undergo bail out procedures (e.g. subtotal cholecystectomy) will be included.)
• be ≥ 18 years old
• be stratified for the risk of CBDS according to the Israelian Score (29), and, in case of confirmation of CBDS receive pre-operative ERCP
• provide signed and dated informed consent form
• willing to comply with all study procedures and be available for the duration of the study.

Exclusion Criteria:

• pregnancy or lactation
• acute cholecystitis not related to a gallstone etiology
• onset of symptoms >10 days before cholecystectomy** (** Patients with ACC associated with common bile duct stones who underwent pre-operative ERCP could be included if they receive EC within 10 days from onset of symptoms)
• concomitant pancreatitis
• intraoperative treatment of common bile duct stones
• anything that would place the individual at increased risk or preclude the individual's full compliance with or completion of the study.

Patients who receive a diagnosis of ACC as defined by TG18 criteria and with ACC candidate to EC during the index admission