The study by Koren and colleagues in this issue addresses several important issues related to the natural course of acute and chronic responses to trauma. One popular theory that led to the inclusion of the avoidance cluster is that the natural course of PTSD is characterized by alternating waves of intrusions and avoidance. Retrospective studies of the natural history of PTSD R1563BJEGABEH, however, found no evidence for this, and the study by Koren et al., which used a superior longitudinal design, corroborated this finding. Rather, the course of PTSD is characterized by a pattern of increase in symptoms soon after the trauma, followed by a plateau, with no evidence of delayed onset or alterations between symptom clusters. The study of Koren et al., however, almost has the disadvantage of being so simple that it is obvious. That is, their finding of a correlation between symptoms at successive points in time is a natural part of any disorder’s progression in time. Another limitation of this study is the lack of assessment of symptoms of acute stress disorder. This study does shed light, however, on important issues of PTSD and comorbidity, showing that depression and non-PTSD anxiety disorders developed in conjunction with PTSD in stress survivors. This is consistent with other data, e.g., from the National Vietnam Veterans Readjustment StudyR1563BJECFJFD, which showed that rates of depression and anxiety disorders (as well as alcohol and substance abuse) are higher in combat veterans with PTSD. On the basis of these findings, comorbid depression should be seen as secondary to PTSD (or a parallel response to trauma) but not as a unique disorder.