A 56-year-old male was treated with sintilimab for their unresectable hepatocellular carcinoma. After eight cycles of sintilimab, the patient experienced polyuria, polydipsia, elevated fast glucose of 22.2 mmol/L (399.6 mg/dL), HbA1c of 7.8%, pH of 7.27, bicarbonate of 12.9 mmol/L, and lactate level of 1.8 mmol/L. The patient was diagnosed with sintilimab-induced new-onset autoimmune diabetes and treated with rehydrate therapy, electrolyte acid-base balance therapy, and insulin. The patient was discharged on insulin aspart and insulin glargine. Here, INS is linked to hepatocellular carcinoma.