A cross-sequential design was used to examine changes related to aging in adults with and without Down syndrome (ns = 55 and 75, respectively). Adults received yearly neuropsychological and medical evaluations. Support for precocious aging in adults with Down syndrome was evident only on a test of verbal fluency, with weaker support obtained on a test of fine-motor skills. Cross-sectional age differences for all adults were obtained on tests of memory and community living skills. General intellectual level, gender, and psychiatric status were consistently related to performance, indicating the need to examine such mediating variables in studies on aging.