Objective: Estimation of premorbid function is essential to accurate identification of cognitive impairments. We explored how lexical tasks can be used to estimate various cognitive functions. Method: Adults with cognitive impairment due to neurological illness (n = 15) and a nonclinical sample of adults (n = 143) completed tests of word pronunciation, lexical decision, and stem-completion naming. In three studies lexical-task performance associations with intelligence Wechsler Adult Intelligence Scale 4th edition (WAIS-IV), episodic memory, executive functioning, and theory of mind were explored. Results: At the group level, word pronunciation was robust in the presence of cognitive impairment. However, as a case series, patients showed idiosyncratic patterns of preservation of lexical skills. All of the lexical tasks were highly correlated with intelligence quotient (IQ) scores in the nonclinical sample, suggesting that they may function well as estimators of premorbid intelligence. Simulated impairments in nonclinical adults revealed that the median score from the three different tasks had the highest correlation with, and provided the most accurate and precise estimates of, measured IQ, and was also the least sensitive to impairment. We also show that these methods predict executive functions, in particular, proverb interpretation, phonemic/semantic alternating verbal fluency, and working memory span performance. Conclusions: Several lexical tasks are potentially useful in predication of preillness cognitive ability. However, due to the heterogeneity of impairments between patients, estimation of premorbid levels could be improved by the use of average estimated values from multiple tests. This could potentially improve diagnostic accuracy and quantification of neuropsychological impairments. (PsycInfo Database Record (c) 2021 APA, all rights reserved) Understanding a patient’s cognitive impairments following brain illness is better if their abilities before the illness can be estimated. Reading that requires preexisting knowledge of the words, such as how to pronounce them, can be used for this purpose. Word pronunciation, particularly when combined with other tests of word knowledge, appears to be not much affected by cognitive impairment and gives a good indication of a patient’s preillness ability.