The aim of this study was to examine the effects of a 6-month intensive lifestyle modification intervention on metabolic parameters and carotid intima-media thickness (IMT) in patients with type 2 diabetes mellitus. Fifty-eight subjects with type 2 diabetes mellitus were randomly assigned to the intervention group or the control group. The subjects in the intervention group participated in a 16-week intensive lifestyle modification program and subsequent monthly meetings during the 6-month study period. Control subjects received basic dietary education and usual care. Anthropometric data, metabolic parameters, and carotid IMT were examined before the intervention and after 6 months. Lifestyle modification intervention group patients showed a significant reduction in HbA1c (-1.0% +/- 1.3% vs +0.1% +/- 1.2%, P = .002), fasting blood glucose (-1.6 +/- 1.5 vs +0.3 +/- 2.5 mmol/L, P = .001), and 2-hour postprandial plasma glucose (-2.1 +/- 2.5 vs +0.8 +/- 4.4 mmol/L, P = .003) compared with control patients after 6 months. Body weight (-2.0 +/- 2.6 vs +0.2 +/- 1.7 kg, P = .001), body mass index (-0.8 +/- 1.0 vs 0.0 +/- 0.8 kg/m2, P = .003), and systolic blood pressure (-8.2 +/- 15.9 vs +0.4 +/- 14.1 mm Hg, P = .041) were significantly decreased in the intervention group. A significantly reduced carotid mean IMT progression was seen in the intervention group after 6 months (-0.040 +/- 0.136 vs +0.083 +/- 0.167 mm, P = .007). Changes in HbA1c (r = 0.34, P = .028), fasting plasma glucose (r = 0.31, P = .045), and 2-hour postprandial plasma glucose (r = 0.37, P = .015) correlated with the mean carotid IMT change after adjustment for age and sex. In conclusion, a 6-month intensive lifestyle modification intervention in patients with type 2 diabetes mellitus resulted in improved glycemic control and decreased progression of carotid IMT.