Premorbid intellectual function estimation is a crucial part of patient evaluation following a traumatic brain injury (TBI), especially in individuals with ADHD who are at higher risk for TBI compared to their non-ADHD peers. This study investigates the value of using regression-based estimates of intelligence for concurrently predicting measured intelligence in a sample of older adolescents with and without a childhood history of ADHD. Correlations between measured and estimated intelligence are highly significant in the full sample and in the individual groups. Adding reading performance to the regression equation increases the accounted-for variance in both groups. Results indicate that regression equations based on demographic characteristics constitute a valid method for estimating premorbid functioning in adolescents with ADHD and that they can play an essential role in the assessment of individuals with ADHD who sustain TBI, especially when measures of word reading are used to augment demographic estimates. (Contains 2 tables.)