AIM: Diabetes mellitus (DM) is an independent risk factor for stroke. In a DM population, carotid atheromatosis is a major cause of stroke. The role of carotid plaque inflammation remains conflicting. Microwave radiometry (MWR) is a new non-invasive method allowing in vivo measurement of the temperature of tissues, so reflecting inflammation. The aim of this prospective study was to evaluate the impact of DM on carotid artery inflammation in patients with documented coronary artery disease (CAD). METHODS: Consecutive patients (n=300) with significant CAD were evaluated by: (1) ultrasound study of both carotid arteries; and (2) the temperature difference (ΔT) along each carotid artery on MWR. ΔT ≥ 0.90 °C was considered high ΔT. Vessel- and patient-based analyses were performed to determine the impact of DM on morphological and functional characteristics of carotid arteries. RESULTS: Out of 300 patients, 113 (37.7%) had DM. Patients with DM had similar carotid plaque thickness compared with patients without DM in both vessel- and patient-based analyses. In contrast, patients with DM exhibited higher ΔT values in both vessel- and patient-based analyses. On multivariate logistic regression analysis, DM was an independent predictor of high ΔT both unilaterally and bilaterally (OR: 1.66, 95% CI: 1.06-2.58, P=0.03 and OR: 1.96, 95% CI: 1.01-3.81, P=0.05, respectively). CONCLUSION: In patients with CAD, DM was an independent predictor of local carotid plaque inflammatory activation. Whether or not the assessment of functional plaque characteristics by MWR can be an additional prognostic tool independent of structural factors now needs to be further investigated.