Recent research suggests that a proportion of women may develop posttraumatic stress disorder after birth. Research has not yet addressed the possibility that postpartum symptoms could be a continuation of the disorder in pregnancy. This study aimed to test the idea that some women develop posttraumatic stress disorder as a result of childbirth, and to provide an estimate of the incidence using a prospective design, which controls for the disorder in pregnancy. This prospective study assessed 289 women at three time points: 36 weeks gestation and 6 weeks and 6 months postpartum. The prevalence of posttraumatic stress disorder was assessed by questionnaire at each time point, and the incidence was examined after removing women who had severe symptoms of posttraumatic stress disorder or clinical depression in pregnancy. After removing women at the first time point, 2.8 percent of women fulfilled criteria for the disorder at 6 weeks postpartum and this decreased to 1.5 percent at 6 months postpartum. The results suggest that at least 1.5 percent of women may develop chronic posttraumatic stress disorder as a result of childbirth. It is important to increase awareness about the disorder and to give health professionals access to simple screening tools. Intervention is possible at several levels, but further research is needed to guide this intervention.