Sintilimab, a monoclonal anti-PD-1 antibody, has been approved in China for the treatment of Hodgkin's lymphoma and was used in our clinical trial for patients with unresectable hepatocellular carcinoma (HCC).<h4>Case presentation</h4>We present the first case of autoimmune diabetes during Sintilimab treatment in a patient with unresectable HCC, accompanied by a remarkable anti-tumor effect of partial regression. The gene discussed is PDCD1; the disease is neoplasm.