Healthy adults with Down syndrome (DS) with mild/moderate mental retardation (MR) were compared to adults with MR from other causes on the WISC-R. Adults with DS <45 years of age did better on the performance subtests than on the verbal subtests. Among the participants with DS the classic aging pattern was observed in which adults 45 years of age had a selective decline on the performance subtests compared to younger participants with DS, while verbal subtest scores remained unchanged. Adults with MR from other causes did not show the same age-associated differences within the same age range. It appears that adults with DS show the effects of aging within their area of relative cognitive strength, that is, in nonverbal abilities. For this group, the effects of normal aging may not only occur earlier, but may also have a greater impact on their overall functioning than for their peers.