Externalizing behaviors (EBs) pertain to a diverse set of aggressive, antisocial, and potentially destructive behaviors directed toward the external environment. They range from nonclinical to clinical in severity, associated with opposition, aggression, hyperactivity, or impulsivity, and are considered a risk factor for the emergence of psychopathology later in adulthood. Focusing on community adolescents (N = 102; 49 female and 53 male adolescents; age range 12-19 years), this study aimed to explore the relations between EBs and the cortical thickness of regions of interest as well as to identify possible risk markers that could improve understanding of the EB construct. Using a mixed cross-sectional and prospective design (1-year follow-up), we report specific associations with cortical thickness of the left insular, right orbitofrontal, and left anterior cingulate cortex. Specifically, thinner left insular and right orbitofrontal cortex was associated with higher EBs, and thinner left anterior cingulate cortex predicted less reduction in EBs 1 year later. In addition, further examination of the aggression and rule-breaking subscales of the Youth/Adult Self-Report, used to assess EBs, revealed specific associations with insular subregions. Findings suggest that cortical structure morphology may significantly relate to the expression and maintenance of EBs within the general population of adolescents.