Even though notable progress has been made in raising awareness of cigarettes in relation to cardiovascular and lung diseases, much less is known about the endocrine effects of nicotine and smoking. The goal of this article is therefore to review the effects of nicotine (Box 1) and cigarette smoking on the endocrine system, by critically evaluating studies in both humans and animal models, and to address areas in need of further research. Gaining a better understanding of the effects of nicotine on the endocrine system and its subsequent impact upon the pathogenesis of various endocrine diseases will allow targeted therapies and provide useful information for the development of more effective approaches for smoking cessation.