Neuropsychological assessment is critically dependent upon comparison to a standard normative database. While generally appropriate for individuals of near-average intelligence, high-intelligence individuals may be erroneously scored as unimpaired and low-intelligence individuals as impaired on cognitive measures. The current paper describes an approach for minimizing such misclassifications that is standardized and practical for clinical use. A computerized test of nonverbal reasoning co-normed with cognitive measures is used for automatic adjustment of normalized cognitive scores. This premorbid estimate showed good construct validity, and adjustment raised cognitive scores for low-intelligence individuals, and lowered cognitive scores for high-intelligence individuals similarly across demographic (age, education, computer experience) and clinical (cognitively healthy, mild cognitive impairment, dementia) subgroups. Adjustment was typically up to three normalized units for scores on the premorbid estimate of +/-1 SD and 6 normalized units for scores of +/-2 SD. The present approach shows promise as a practical solution for assessment of high- and low-intelligence individuals.