In this issue, Jensen et al (Epidemiology. 2007;18:220–225) publish new evidence linking maternal smoking with cryptorchidism. These new data make the cumulative evidence for a true association persuasive enough to be seriously considered. Possible biologic mechanisms may include endocrine disruption by cigarette smoke, although the role of endocrine disruptors in cryptorchidism more generally has been inconsistent. There are important research questions suggested by the link between mother’s smoking and cryptorchidism, including a possible role of father’s smoking, the role of genetic susceptibility, and the effects of mother’s smoking on further aspects of her son’s reproductive health.