Carotid intima-media thickness has been widely used as a surrogate end-point for cardiovascular disease, myocardial infarction, and stroke. This study aimed to assess the effects of active and passive smoking exposure on the development of cardiovascular disease in patients with type 2 diabetes mellitus. Seven hundred twenty-two patients with type 2 diabetes mellitus were recruited for the study. A standardized questionnaire on smoking status, pack-years of smoking, and the number of years of smoking cessation was provided to the patients, and their responses were collected for analysis. The carotid intima-media thickness, carotid plaque, and the internal diameter of the common carotid artery were determined by high-resolution B-mode ultrasonography. Compared to non-smokers, passive female smokers had a higher risk of cardiovascular disease (odds ratio = 3.50, 95% confidence interval:1.29–9.49,P =0.009); they also had a significantly larger common carotid artery (P= 0.041) and risk of carotid plaque (odds ratio = 2.20, 95% confidence interval:1.1980–4.0505,P =0.01). Both active and passive male smokers had a significantly greater carotid intima-media thickness than non-smokers (P =0.003 andP =0.005, respectively). Male active smokers had a significantly higher risk of carotid plaque (odds ratio = 2.88, 95% confidence interval:1.4788–5.6094,P =0.001). In conclusion, cumulative active and passive smoking exposures are significant risk factors for carotid atherosclerosis in patients with type 2 diabetes mellitus. Our results highlight the importance of endorsing a smoke-free environment for patients with type 2 diabetes mellitus.