We tested whether familial aggregation of Down syndrome and Alzheimer's disease (AD) is present for trisomies of other autosomes. We compared rates of Alzheimer-like dementia in the parents of women with trisomic pregnancy losses (n= 109) with those in parents of women with chromosomally normal losses (n= 151) and births (n= 216). Relative risks of Alzheimer-like dementia in parents of women with trisomic losses were 1.2 (95% Cl 0.6, 2.2) and 0.9 (95% Cl 0.5, 1.5) in comparison to parents of women with chromosomally normal losses and births, respectively. Associations were similar among women whose index pregnancy occurred before age 35 or later. Our data do not support an association between the occurrence of AD and trisomy of all autosomal chromosomes. They raise the possibility that familial aggregation with AD is specific to trisomy 21.