Genetic analysis has allowed the dissection of the pathogenic pathway that leads to Alzheimer's disease. It has also been integral to the development of earlier and more accurate diagnostic practices. This analysis has identified many potential therapeutic targets, and clinical trials aimed at these targets are now under way. If these approaches are successful, it will be a spectacular validation of genetic-knowledge-based treatment strategies; if they are not, researchers will need to re-evaluate this approach toward understanding and developing strategies for treating complex diseases.