Statistical analyses were performed with SPSS Version 13.0 for Windows (SPSS Inc, Chicago, IL). Hippocampal volumes were analyzed with a repeated-measures analysis of variance. Also, two-tailed, paired-sample t-tests were used to compare hippocampi, clinical assessments on CAPS total score, and each subscale of the CAPS before and after treatment. An alpha level of 0.05 was used for all statistical tests. The analysis showed that there was a significant difference in hippocampal volumes after the treatment (F=11.70; df=1,8; p=0.009) and a significant difference between the two sides (F=18.95; df=1,8; p=0.002), but no interaction between treatment phase and side (F=0.11; df=1,8; p=0.742). Detailed analyses indicated that there was an increase in both the left (+6.5%; t = –3.27; df=8; p=0.011) and the right side (+6.3%; t = –3.34; df=8, p=0.010; Table 1). After treatment, we also observed an improvement in PTSD symptoms as measured with CAPS total score (−65.3%; t=4.78; df=8; p=0.001), and on the three CAPS subscales (Table 1). After the treatment, all subjects no longer met the SCID criteria for PTSD. Despite these promising results, we acknowledge that the present study is only a pilot study because it has several limitations. First, the sample size was small. Second, there was no control group (this choice was motivated by ethical reasons). Third, we do not know whether the increase in hippocampal volume was caused by a promotion of neurogenesis or other reasons, such as, for example, a change in water content in the hippocampus. Despite these limitations, the results of this preliminary study suggest further consideration of the potential effects of psychotherapy on the neurobiology of psychiatric disorders, and not dismissing the question of whether psychotherapy may have beneficial effects on hippocampal structure. Further studies should be carried out in order to validate the present results, possibly with a larger sample of PTSD subjects, a control group, and different types of psychotherapy.