PIP: This article reviews currently available epidemiologic and experimental data on the effects of cigarette smoking on reproductive health. Specifically addressed are the evidence for and possible physiologic causes of disturbance in 3 areas: female fertility, male fertility, and the effect of smoking on reproduction and pregnancy. Approximately 30% of women and 36% of men of reproductive age in the US are smokers. The literature offers clear support for an association between smoking and decreased female fecundity and fertility, especially with a relationship to primary tubal infertility. Cigarette smoke appears to have adverse effects along a continuum of preimplantation and implantation reproductive processes, including gamete production and function, ovulation and cyclicity, fertilization, early embryonic cleavage, embryo transport, and implantation. In men, there is clear evidence that smoking results in fewer and less motile sperm as well as a lower proportion of normally shaped sperm; however, it remains unclear whether this impairment in spermatogenesis results in clinical impairment of fertility. Studies have demonstrated a significant increase among smoker both in the risk of spontaneously aborting a chromosomally normal fetus and in the risk of spontaneously aborting a chromosomally normal fetus and in the risk of prematurity. Moreover, smoling has been shown to cause a 150-300 gram decrease interm infant birthweight. Al these risks to fecundity and pregnancy outcome are minimized or absent in former smokers. It is stressed that efforts to persuade women to stop smoking have been inadequate. It is particularly imperative for women who have had divviculties conceving or have had a history of miscarraiges to give up cigarette smoking.