1. The WAIS-R short form used on the second testing occasion probably overestimates the full-scale IQ of schizophrenic patients because it does not include several subtests on which poor performance is common among this group. To address this issue empirically, I examined the WAIS-R performance of 103 schizophrenic patients at the National Institute of Mental Health (NIMH). The group's mean full-scale IQ was 88.3 (SD=11.9) with a score of 97.5 (SD=88.3) on the Wide-Range Achievement Test-Revised; those scores suggested a 9.1-point decline (matched pair t test: t=8.15, df=102, p<0.0001). The patients' performance on Russell et al.'s five-subtest short form (mean=8.77, SD=2.2) differed significantly (t=6.53, df=102, p<0.001) from their performance on the remaining six subtests (mean=8.02, SD=1.9) as well as on all 11 subtests (mean=8.40, SD=2.0). This significant difference occurred despite a high correlation (r=0.94) between short-form and full-scale IQs. Thus, subjects retained their relative positions across short-form and full-scale IQs, but the short-form estimates were systematically higher than the actual full-scale IQs. Because all WISC-R subtests were administered at time 1, the comparison of actual WISC-R full-scale IQ versus short-form WAIS-R IQ is biased against detecting differences.