OBJECTIVE We have previously shown that chronic inflammation results in immunosuppression associated with CD247 downregulation in T lymphocytes. Type 2 diabetes mellitus (T2DM) is known to be associated with chronic inflammation. We therefore sought to examine CD247 expression levels in patients with T2DM and to assess whether it can serve as a diagnostic and prognostic biomarker for disease complications and outcomes. RESEARCH DESIGN AND METHODS Peripheral blood samples from 75 T2DM patients and 40 healthy control subjects were collected and analyzed for the expression level of CD247 in T lymphocytes. Subjects with T2DM underwent a medical interview with physical examination and were followed for an additional average of 19.2 ± 0.9 months to determine the occurrence of major adverse disease end points. The relationship between the level of CD247 expression and disease status at the time of blood draw and the ability of the marker to identify future complications was evaluated. RESULTS We observed a significant reduction in CD247 expression levels in T lymphocytes of T2DM patients when compared with healthy volunteers. CD247 downregulation was associated with disease severity, complications, and the occurrence of future cardiovascular events, suggesting its potential use not only as a diagnostic but also as a prognostic biomarker. CONCLUSIONS Our results suggest the use of CD247 as a biomarker in diabetic patients for evaluating the state of chronic inflammation that contributes to morbidity and mortality in this disease and for the prediction of future cardiovascular events.