Smoking increases insulin resistance via multiple mechanisms but is a poorly understood risk factor for onset of type-2 diabetes. It is also associated with impaired beta-cell function in humans, but again the mechanisms are poorly understood. Mechanistic studies of the impact of smoking on carbohydrate metabolism mainly evaluated nicotine as the causal agent, and more rarely other tobacco constituents, making it impossible to conclude that the risk of diabetes is linked to the effects of nicotine alone. Active smoking also has negative impact on glycemic control in both type-1 and type-2 diabetic patients. It increases the risk of all-cause mortality and worsens the chronic complications of diabetes. Impact on microangiopathic complications in type-2 diabetic patients, however, is more controversial. Data on pharmacological and behavioral strategies for smoking cessation used in the general population are more sparse in diabetic patients, despite opportunities with recent therapeutic trials involving varenicline and GLP-1 analogues. It is essential for diabetic patients to stop smoking, and diabetologists must get involved in smoking cessation as they have done for many years in therapeutic education, which can easily include measures to help patients stop smoking.