The life expectancy of people with mental retardation has dramatically increased over the past several decades. However, relatively little attention has been paid to the phenomenon of aging in this population, largely due to the historic fact that few of these people survived to become senior citizens. A rapidly expanding population of older adults with lifelong histories of atypical development may require unique patterns of services. Vulnerability to Alzheimer's disease is among the specific concerns that will need to be addressed. Because adults with Down syndrome exhibit many indications of accelerated aging, including a substantially increased risk for Alzheimer's disease, it is particularly important to understand their patterns of aging. Literature relevant to these issues is reviewed.