For decades, researchers have worked to better understand why women are about twice as likely as men to develop posttraumatic stress disorder (PTSD). We know that differences in trauma exposure explain part of that disparity. Women are more likely to experience certain types of trauma, including sexual assault and childhood sexual abuse, both of which carry a particularly high risk for developing PTSD. But that has never been the whole story. Increasingly, researchers are asking another question: Could the natural hormonal changes women experience throughout life also influence how PTSD symptoms are experienced? While this area of research is still evolving, studies published over the past decade have begun pointing in a similar direction. From the menstrual cycle to pregnancy and the menopausal transition, researchers are finding that women’s reproductive biology may be a more important part of understanding PTSD than previously recognized.