Background <p>The incidence of type 1 diabetes caused by immune checkpoint inhibitors is very low, and the co-occurrence of immune myocarditis is even rarer. Immune checkpoint inhibitors can lead to irreversible damage to beta cells, increasing the risk of diabetic ketoacidosis. Myocarditis occurring during treatment with immune checkpoint inhibitors is a rare but potentially fatal event, with a high mortality rate, requiring heightened clinical vigilance. This paper reports a case of toripalimab-induced immune myocarditis complicated with type 1 diabetes.</p> Case presentation <p>A 66-year-old male patient with a yellow complexion presented with uncontrolled glycemic levels for a duration of 6&#xa0;months. The patient had previously been diagnosed with intrahepatic cholangiocarcinoma and cardiac insufficiency. Regular immunotherapy treatment was administered using toripalimab at a dosage of 240&#xa0;mg. Laboratory data obtained during the course of treatment revealed C-peptide levels below 0.01&#xa0;ng/mL, while cardiac ultrasound and resting myocardial perfusion imaging indicated evidence of myocardial injury. Based on auxiliary examination results, it was suggested that the patient’s islet cell function had been compromised and myocardial injury was present. The patient’s history of receiving toripalimab for intrahepatic cholangiocarcinoma aligned with immune-related adverse events associated with immune checkpoint inhibitors, leading to the diagnosis of type 1 diabetes mellitus accompanied by immune myocarditis caused by immune checkpoint inhibitors.</p> Conclusion <p>This article presents a case study of immune-mediated myocarditis developing alongside type 1 diabetes after 1&#xa0;year of toripalimab treatment. The analysis aims to facilitate early detection and mitigation of adverse reactions while emphasizing the need for heightened vigilance among clinical practitioners regarding immunosuppressant usage.</p>