Background The insula is involved in interoceptive processing, emotion awareness, and attention to salient stimuli. Research suggests that these functions are specific—albeit overlapping—within insula subdivisions. Additional studies also imply that sexual dimorphism and different rates of development occur within these subdivisions in youth. The purpose of this study was to examine potential insula subdivision structure differences in youth with PTSD symptoms as compared to controls and test sex as a moderator of these differences. Methods Insula structure (volume, surface area, and thickness) was measured with structural magnetic resonance imaging (sMRI) and calculated using Freesurfer software. We compared insula structure across age‐ and sex‐matched boys and girls with (30 with and 29 without) PTSD symptoms while also controlling for age and whole brain measurements. Results Differences were specific to the insula's anterior circular sulcus. Within this subregion, boys with PTSD symptoms demonstrated larger volume and surface area than control boys, while girls with PTSD symptoms demonstrated smaller volume and surface area than control girls. Discussion Findings indicate a potential neurobiological explanation for sex differences in youth with PTSD symptoms.