We recently examined the brain from an 8-month-old infant with Down's syndrome and found argyrophilic plaque-like deposits throughout the neocortex and cerebellum. To ascertain the specificity of this observation, we examined 27 additional brains from the pediatric autopsy service, including 1 from another patient with Down's syndrome. To our surprise, similar argyrophilic deposits were found in 16 of these cases. The deposits were equally well stained by three different silver stains and had the same size, shape, and distribution in gray matter as the diffuse amyloid plaques commonly seen in adults. However these structures appeared to be amyloid negative. There were no obvious differences in the primary diagnoses amongst the group of patients with argyrophilic deposits and the group without them, and the origin, permanence, and functional significance of these plaque-like deposits are still unknown. Nonetheless, their recognition is important since they may represent subtle brain injury and since similar structures in adults might easily be misinterpreted as true diffuse amyloid plaques.