Evidence suggests that the anterior cingulate cortex (ACC) plays a key role in the development of posttraumatic stress disorder (PTSD). Owing to the region's highly variable patterns, three different studies of PTSD have yielded inconsistent volume reductions. Accordingly, in order to measure the correct borders and volumes, the different patterns of the ACC must be considered separately. We examined 15 victims with chronic symptoms of PTSD, all traumatized at the same accident in 1988, comparing them to 15 matched control subjects. After categorizing the ACC according to single, single segmented, double or double segmented cingulate sulcus (CS), we measured the area with a semi-automated procedure using Brain2 software. Fifty-three percent of our PTSD subjects had single segmented CS compared to 23% in control subjects and 25% in the literature. Furthermore, the four patterns showed differences in mean volume over all subjects of up to 13%. We detected no differences in absolute ACC volumes when differentiating between the patterns or in correlation with brain volumes or clinical parameters. This is the first study to differentiate ACC structure into different patterns in PTSD. We found that one pattern was overrepresented which, in turn, could signal vulnerability to develop PTSD. Because of the remarkable volume differences between patterns, future studies should categorize this highly variable region into different patterns for volumetric measurements. However, future investigations in larger samples should confirm our findings and assess to which extend alterations of ACC patterns may influence the incidence of PTSD.