© 2018Volume-based hippocampal findings in Social Anxiety Disorder (SAD) and Posttraumatic Stress Disorder (PTSD) have been inconsistent, with very little investigation of hippocampal subfields. We assessed the effects of early childhood trauma on hippocampal subfields in participants with SAD with and without early childhood trauma and PTSD, compared to healthy controls. The sample comprised 26 participants SAD with early childhood trauma, 22 participants with SAD without early childhood trauma, 17 with PTSD secondary to early childhood trauma and 25 control participants. We used Freesurfer version 6 to determine hippocampal subfield volumes. Findings included significant reduction in right parasubiculum volume between the PTSD group secondary to early childhood trauma and the SAD group without early childhood trauma, as well as a significant reduction in left HATA (Hippocampal Amygdala Transition Area) volume between PTSD with early childhood trauma compared to controls, as well as compared to SAD with early childhood trauma. These findings did withstand correction for multiple resting using the false discovery rate. Our findings of an association of reduced volumes in the parasubiculum and HATA regions with PTSD secondary to childhood trauma are interesting. Further work should investigate whether parasubiculum and HATA regional volume reductions in PTSD are a specific effect of early childhood trauma or a specific manifestation of PTSD pathology. Further work should also be undertaken to determine if hippocampal subfield atrophy is associated with SAD in the setting of early childhood maltreatment.