A 47-year-old man presented with a 1 week history of progressive fatigue and decreased appetite. He had stage IV oral squamous cell carcinoma and was treated with sintilimab, a programmed cell death protein 1 inhibitor, 22 months earlier. Laboratory work-up revealed significant elevation of bilirubin, liver enzymes, glucose, and lipase. Ultrasound examination and magnetic resonance cholangiopancreatography showed severe stenosis and occlusion of the pancreatic segment of the common bile duct, and PET/CT revealed swelling of the pancreas with diffuse increase in glucose metabolism. He was diagnosed with immune checkpoint inhibitor (ICI)-related pancreatitis and the treatment with sintilimab was permanently discontinued. He was administered systemic methylprednisolone at a dose of 2 mg/kg/day and subcutaneous insulin injection, without intravenous fluid or protease inhibitor. He improved quickly and received oral methylprednisolone for 10 months in gradually decreasing doses. He maintained well at 20 month follow-up. ICI-related pancreatitis is rare and varied. Further studies are needed to investigate the differences in the two types of ICI-related pancreatitis: acute pancreatitis and autoimmune pancreatitis-like cases.