Information regarding cognitive abilities in earlier stages of life is essential to ascertain if and to what extent these may have declined. When unavailable, clinicians rely on estimate methods. One of the contemporary methods used worldwide combines performance on irregular word reading test with demographics since it has shown to provide reliable estimates of premorbid ability. Hence, a reading test portuguese irregular word reading test (TeLPI) was developed, filling an important gap in the neuropsychological evaluation of Portuguese speakers. Using 46 irregular, infrequent Portuguese words, TeLPI was validated against Wechsler Adult Intelligence Scale (WAIS)-III (N = 124), and regression-based equations were determined to estimate premorbid IQ considering TeLPI scores and demographic variables. TeLPI scores accounted for 63% of the variance of WAIS-III Full-Scale IQ, 62% of Verbal IQ, and 47% of Performance IQ and thus were considered valid for premorbid intelligence estimation.