Objective While there is a wealth of research into the Flynn effect, as yet no research exists examining the effect on tests of premorbid functioning. This study investigated the ability of the National Adult Reading Test (NART), the Wechsler Test of Adult Reading (WTAR), and the Test of Premorbid Functioning (TOPF) to predict premorbid IQ. It was hypothesised that the tests of premorbid functioning would produce differing premorbid IQ estimates, with the NART predicting the highest premorbid IQ scores, followed by the NART‐2 and the WTAR, with the TOPF predicting the lowest scores. Method Ninety‐five unimpaired Australian male and female participants aged between 18 and 65 years were administered a comprehensive battery of tests, including each of the tests of premorbid functioning. Results Results indicated that premorbid IQ estimates were significantly different (p < .001) from each other, with the NART producing the highest premorbid IQ estimate and the TOPF the lowest estimate. Conclusions These findings indicate that premorbid estimates of functioning are subject to the Flynn effect, thus use of estimates produced by tests of premorbid abilities that were designed to predict to earlier editions of the Wechsler scales will tend to inflate the level of premorbid baseline, leading to the possibility of spurious diagnosis of deficit. Clinicians should employ the most recently normed versions of these tests and employ the premorbid estimate which has been validated to predict the edition of the Wechsler scales that the individual will actually be using during any testing.