BACKGROUND We aimed to evaluate the characteristics of carotid artery plaques and the relationship between intraplaque neovascularization (IPN) and hemoglobin A1c (HbA1c) in patients of <60 years old with diabetes mellitus (DM) by comparison with diabetes ≥60 years of age. METHODS One-hundred-and-one patients with DM were studied into two groups: those <60 and those ≥60 years of age. All the patients underwent standard carotid ultrasonography and contrast-enhanced ultrasonography, which we used to evaluate IPN. RESULTS Diabetic complications were present in 41 of 50 patients (82 %) in the <60-year-old group, of whom 17 (34 %) had diabetes-related vascular complications. Of the 47 plaques in the <60-year-old group, six (13 %) had IPN Grade 0, 16 (34 %) had IPN Grade 1, and 25 (53 %) had IPN Grade 2. The AUC and RAUC of the plaque in the <60-year-old group were significantly higher than those of the ≥60-year-old group (P = 0.012 and 0.031, respectively). There were also differences in the AUC, RAUC and semi-quantitative grades between patients with and without diabetic macrovasculopathy and diabetic peripheral artery disease (all P < 0.05). The AUC, RAUC and semi-quantitative grading of IPN positively correlated with blood glucose and HbA1c (P < 0.05). CONCLUSIONS IPN is more common in DM patients who are younger, and have higher blood glucose and HbA1c concentrations, and these plaques are more vulnerable.