We review the current status as well as the risks and benefits of a recently developed DNA test of risk for Alzheimer's disease: the apolipoprotein E genotype. While apolipoprotein E genotypes may indicate a degree of susceptibility, the gene is neither necessary nor sufficient to cause the disease; thus, many questions remain. Because risk prediction is not straightforward, practical issues related to the testing of complex diseases like Alzheimer's and to the ethical, legal, and social implications of genetic tests require careful consideration and unambiguous answers. The use of apolipoprotein E genotyping in patients with Alzheimer's disease should be limited to research centers, and additional studies are strongly recommended. Apolipoprotein E genotypes should not be available to third parties such as insurers or employers until genotypic risks are fully understood. National policies that encourage scientific investigation while maintaining individual privacy and limiting unnecessary access to genetic information should be immediately developed.