We investigated a possible imbalance between T helper (Th)17 and CD4+ CD25+ forkhead/winged helix transcription factor (Foxp3) T regulatory (Treg) cells in patients with carotid artery plaques. From November 2009 to September 2010, we enrolled 126 males and 104 females with mean age 68.24 +/- A 6.71 years. Based on carotid artery sonography, the 230 subjects were categorized into three groups: plaque negative; stable plaques; and unstable plaques. Th17 and Treg cell frequencies, relevant plasma cytokines (IL-17, IL-6, IL-23, and TNF-alpha), and ROR gamma t mRNA levels were determined. Compared to plaque negative, Th17 cells, Th17-related cytokines (IL-17, IL-6, IL-23, and TNF-alpha), and ROR gamma t mRNA levels were higher with stable plaques, and highest with unstable plaques. The opposite trend was found for Treg cells, Treg-related cytokines (IL-10 and TGF-beta 1), and Foxp3 mRNA. Th17 cell frequencies were significantly negatively correlated with Treg cell frequencies. Our investigation demonstrated that there is a Th17/Treg functional imbalance in patients with unstable carotid atherosclerotic plaques. Th17 cells may promote atherogenesis, while Treg cells may have a protective role against atherosclerosis plaques. An imbalance of Th17/Treg cells may offer a new direction for the treatment of atherosclerosis.