This study investigated the relationship between carotid plaque neovascularization and diabetes mellitus (DM) by using contrast-enhanced ultrasonography. Contrast-enhanced ultrasonography was performed in 104 patients with carotid plaque thicker than 2.0 mm. There were 36 patients with DM and 68 patients without DM. The enhanced intensity in the plaque and the ratio of enhanced intensity in the plaque to that in the lumen of the carotid artery in patients with DM were significantly greater than those in patients without DM. Our study demonstrated that the enhanced intensity in patients with DM is greater than that their counterparts without DM, suggesting that carotid plaque in DM patients may have more neovessels and may be more vulnerable.