The goal of this review is to determine the effects of smoking on diabetes mellitus, whether it aggravates diabetic complications or influences insulin metabolism and action. Also available anti-smoking programmes applicable for diabetic patients have been studied. The prevalence of smoking among diabetic patients has been investigated by conducting a meta-analysis. Compared with normal subjects, the prevalence of smoking among diabetic patients is significantly higher (27 vs. 33%, p < 0.0001), IDDM patients largely accounting for this difference. However, care must be used in interpreting these data. Smoking presents an extra risk for development of macro- and microvascular complications in these patients, contributing to increased cardiovascular morbidity and mortality. Smoking also increases the risk of diabetes itself. Neither acute nor habitual smoking causes substantial changes in insulin sensitivity in IDDM patients, whereas it does so in NIDDM. Studies in diabetic patients concerning anti-smoking strategies are scarce and only yield disappointing results. Making these patients abstain from smoking turns out to be extremely difficult, probably due to the considerable psychosocial stress experienced.