BACKGROUND: The increasing number of type 2 diabetes mellitus (T2DM) patients leads to higher rates of morbidity and mortality related to lung cancer. AIM: To investigate the utility of the proliferating cell nuclear antigen Ki-67 in patients with lung adenocarcinoma METHODS: One hundred patients with AIS and T2DM (group A), 100 patients with AIS alone (group B), and 60 patients with benign lung lesions (group C) admitted to the Department of Thoracic Surgery and Endocrinology of the First Affiliated Hospital of Soochow University from November 2021 to December 2022 were enrolled. Ki-67 expression was compared among the groups. RESULTS: Group A had significantly higher levels of fasting plasma glucose (FPG), total cholesterol (TC), total triglyceride, low-density lipoprotein cholesterol, glycosylated hemoglobin (HbA1c), and insulin than groups B and C ( CONCLUSION: Ki-67 expression was higher in patients with AIS complicated by T2DM than in patients with AIS alone. Therefore, detecting the Ki-67 level might assist in the diagnosis of AIS in patients with T2DM.