This study evaluated relationships of the Mayo-Portland Adaptability Inventory (MPAI) to the Disability Rating Scale (DRS), the Ranchos Los Amigos Levels of Cognitive Functioning Scale (Rancho), and cognitive performance measures. The Spearman correlation between the MPAI and the DRS was high (rho = .81). Both the MPAI and the DRS differed significantly among patient groups based on independent Rancho ratings (P<.001 for the Kruskal-Wallis test). Spearman correlations between MPAI scores and cognitive performance measures were generally moderate to good (rho >.40), although cognitive performance measures correlated more highly with MPAI cognitive items than noncognitive items. Contrary to expectation, MPAI noncognitive total score was significantly related to a measure of verbal intelligence, but not to measures of verbal declarative memory. These results suggest the possible importance of the fund of academic and social knowledge and the relatively smaller contribution made by verbal declarative memory to overall functional adaptation after brain injury. Results provide initial evidence of the usefulness and concurrent validity of the MPAI as a measure of adaptive functioning after brain injury.