What causes postpartum depression in parents? Hormonal changes, the aftermath of a difficult labor, and genetic predisposition may all play a role, though the research that shows a substantial rate of depression in fathers argues against hormones as the major cause. As a parent as well as a pediatrician, I've always thought that sleep deprivation may be an important trigger. I was pleased to come across a review by Verinder Sharma and Dwight Mazmanian of the University of Western Ontario and Lakehead University addressing this question. In a quiet and delicate way, this paper brings together many small studies that collectively suggest that significant sleep loss may, indeed, contribute to the development of serious postpartum depression. Exploring this possibility might well lead to new ways to diagnose, treat, and even prevent PPD.