In this issue of THE JOURNAL, the article by Thompson and colleagues1 estimates the burden of annual influenza mortality and provides much new and challenging information. The basic mortality question under consideration is what causes excess deaths during annual winter influenza "seasons"? Such mortality excesses can be estimated reasonably well from available data, but it is another problem entirely to determine what proportion is actually due to influenza. Traffic deaths, fire deaths, and other death categories can also increase during the same months.