There is evidence that anterior cingulate cortex (ACC) function is related to individual differences in temperament. An important question regards how early such brain-behavior associations emerge. We examined the relationship between cortical folding patterns of the ACC, which are functionally relevant and primarily determined by birth, and individual differences in four core temperament dimensions (Effortful Control, Negative Affectivity, Surgency, and Affiliation). Magnetic resonance imaging was used to classify 153 (81 male) early adolescents as displaying a leftward asymmetric, rightward asymmetric, or symmetric pattern of ACC folding, as indexed by the incidence and extent of the paracingulate sulcus (PCS). A leftward asymmetric pattern of ACC folding was associated with significantly higher temperamental Effortful Control and lower Negative Affectivity than a rightward asymmetric pattern. Further, this difference was significant only for males. Across males and females, a symmetric pattern was associated with higher temperamental Affiliation than was a rightward asymmetric pattern of ACC folding. These findings suggest that early neurodevelopmental processes contribute to individual differences in temperament. They also illustrate sexual dimorphisms in the neural underpinnings of temperament.