Since the seminal paper by Bremner et al. in 1995 reporting the findings of reduced hippocampal volumes in Vietnam combat veterans, other groups have examined brain morphology in posttraumatic stress disorder (PTSD). However, it is often difficult to compare these studies directly because of differences in types of trauma, length of trauma exposure, age of trauma exposure, and sex. Despite these limitations, many authors have found volume reduction in the hippocampus, suggesting that a structural brain deficit may either predispose to the development of PTSD or be the result of the disorder, or both. In fact, some findings argue that the relatively smaller hippocampal volume in patients with PTSD is a risk factor for the development of PTSD, whereas other findings suggest that hippocampal volume reduction may occur as a result of either stress exposure or PTSD. Regardless of the etiology of the hippocampal volume reduction, early work hints that pharmacological intervention may alter hippocampal volume. This review evaluates and categorizes the existing research of hippocampal volume reduction in patients with PTSD. Other structural brain abnormalities related to PTSD are reviewed. Finally, clinical implications of hippocampal volume reduction in PTSD are considered, particularly the response of the hippocampus to pharmacological intervention.