Metacognition refers to the ability to discriminate between one's own correct and incorrect decisions. The neurobiological underpinnings of metacognition have mainly been studied in perceptual decision-making. Here we investigated whether differences in brain structure predict individual variability in metacognitive sensitivity for visuomotor performance. Participants had to draw straight trajectories toward visual targets, which could unpredictably deviate around detection threshold, report such deviations when detected, and rate their confidence level for such reports. Structural brain MRI analyses revealed that larger gray-matter volume (GMV) in the left middle occipital gyrus, left medial parietal cortex, and right postcentral gyrus predicted higher deviation detection sensitivity. By contrast, larger GMV in the right prefrontal cortex but also right anterior insula and right fusiform gyrus predicted higher metacognitive sensitivity. These results extend past research by linking metacognitive sensitivity for visuomotor behavior to brain areas involved in action agency (insula), executive control (prefrontal cortex) and vision (fusiform).