A matched samples design was employed to compare the British versions of the WAIS (Wechsler, 1955; Saville, 1971) and WAIS-R (Wechsler, 1981; Lea, 1986) in terms of test difficulty. The WAIS yielded significantly higher IQs than the WAIS-R. The mean difference for Full Scale IQ was 8.2 IQ points, i.e. over half a standard deviation. Encouragingly for U.K. users of the Wechsler Scales, additional analysis suggested that the performance of the WAIS-R sample was consistent with an estimated U.K. population mean ∼ 100.