Background Although current guidelines recommend cholecystectomy during the same admission in patients with mild acute biliary pancreatitis (ABP), it involves a waiting list most of the time. Aim We aimed to assess the risk of gallstone-related biliary events (GRBEs) such as cholecystitis, cholangitis, and pancreatitis during the waiting period for cholecystectomy and determine predictors of complications after the first episode of ABP. Methods A prospective observational study was conducted at

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... a tertiary hospital for six months in patients with mild ABP. Follow-ups were done by phone calls or using electronic health records for a maximum of 6 months after discharge or until cholecystectomy. Results A total of 194 patients were included in the study. Although all patients were referred to surgeons, only 81 (41.8%) underwent cholecystectomy within 6 months after discharge. During the observation period, GRBEs developed in 68 (35.1%) patients which included biliary colic, recurrent ABP, acute cholecystitis, choledocholithiasis, gallbladder perforation, cholangitis, and liver abscess. The overall readmission rate was 25.2%, and 44.8% occurred within 4 weeks after discharge. The odds ratio of any complication was 1.58 (95% CI; 1.42-1.76, p=0.028) and 1.59 (95% CI; 1.42-1.78, p=0.009) in the patients who did not have surgery within 2-7 days and 8-15 days, respectively. There was a 4-fold increased risk of readmission (95% CI; 1.16-13.70, p=0,019) if cholecystectomy was not performed within 31-90 days. The patients who developed complications had significantly higher C-reactive protein levels at admission, longer waiting time for cholecystectomy, and had three or more gallstones on imaging than those who did not develop complications. Conclusion Interval cholecystectomy was associated with a high risk of complications during the waiting period in patients with mild ABP.