Patients with Alzheimer disease (AD) show visual impairments in color discrimination (blue hues), stereoacuity, and contrast sensitivity. We asked whether the AD-type visual profile occurs in Down syndrome (DS) in light of the fact that AD neuropathology is present in DS by age 40. We tested 22 adults with DS and 18 adults with mental retardation of non-DS etiology (MR). DS subjects made more tritanomalous errors on the test of color vision than predicated by chance (p < 0.05), indicating a deficiency in the discrimination of short wavelengths (blue hues) but not more of other types of hue discrimination errors. DS subjects had higher stereoacuity thresholds than MR subjects (p < 0.01) and reduced contrast sensitivity across the frequency range (p < 0.01). Taken together, the results point to AD-like visual deficits in DS. Like classic AD, DS may be associated with pathological changes in the parastriate and peristriate visual cortex. DS performance was not correlated with age, suggesting that in individual subjects, the AD-like visual deficits may present prior to and independent of age-associated dementia.