The British picture vocabulary scales (BPVS-II) and the Leiter international performance scales (Leiter-R), both restandardised in 1997, are often used in experimental studies to match individuals with intellectual impairment. Both provide a brief measure of mental age, and cover a wide ability range using a simple format. The BPVS-II assesses verbal comprehension and the Leiter nonverbal abilities. The issue is which to choose. People with Down syndrome (DS), for example, have particular problems in language and so the BPVS may provide an underestimation of ability. The present study investigated this by comparing the performance of 46 young people with DS (21 females, 25 males, mean age 19 years 10 months) on the BPVS-II (verbal mental age VMA) and the Leiter-R brief IQ (nonverbal mental age NVMA). Results Contrary to expectations VMAs were significantly higher than NVMAs (6 years, 6 months and 5 years, 2 months, respectively). There was a significant correlation of 0.61 between the VMA and NVMA, and both discriminated participants at all levels of ability. However, the Leiter-R brief IQ scores provided poor discrimination at the bottom end of the IQ range (IQ 36). Both the BPVS-II and the Leiter-R provide mental age equivalent scores that are useful for plotting developmental progress, although absolute mental ages may differ.