OBJECTIVE: To examine metacognitive ability (MC) following moderate to severe traumatic brain injury (TBI) using an empirical assessment approach and to determine the relationship between alterations in gray matter volume (GMV) and MC. METHOD: A sample of 62 individuals (TBI n=34; HC n=28) were included in the study. Neuroimaging and neuropsychological data were collected for all participants during the same visit. MC was quantified using an approach borrowed from signal detection theory (Type II AUROC calculation) to evaluate judgments during a modified version of the WAIS-III, Matrix Reasoning subtest where half of the items were presented randomly and half were presented in the order of increasing difficulty. Retrospective confidence judgments were collected on an item-by-item basis. Brain volumetric analyses were conducted using FreeSurfer software. RESULTS: Analyses of the modified Matrix Reasoning task data demonstrated that HCs significantly outperformed TBIs [ordered: d = 0.63; random: d = 0.58]. There was a significant difference between groups for MC for the randomly presented stimuli (d = 0.54) but not the ordered stimuli. There was an association between GMV and MC in the TBI group between the right orbital region and MC (R(2) = 0.11). In the HC group, there were associations between the left posterior (R(2) = 0.17), left orbital (R(2) = 0.29), and left dorsolateral regions (R(2) = 0.21) and MC. CONCLUSIONS: These results are consistent with previous research on MC in the cognitive neurosciences, but this study demonstrates that injury may moderate the regional contributions to MC. PUBLIC SIGNIFICANCE STATEMENT: TBI is a great public health concern, as millions of people sustain head injuries each year. This study examines whether individuals who have a TBI also have deficits in monitoring their mental processes (i.e. MC), which has important implications for functional outcome after injury.