Many people who are perfectly relaxed cruising our nation's highways become jittery when they get on an airliner—although most know full well that flying is safer than driving. The statistics are indeed clear on this point. For example, we and a colleague, Dan Weintraub, published a paper in 1991 that documented the substantially lower risk of flying compared with driving in the United States. Some of the many millions of Americans who flew over the next few years probably derived comfort from such hard facts. But now, a decade later, things have changed: The hijacking of four large jets on September 11, 2001, and the disastrous events that ensued led many to forgo flying in the United States during the following months. For example, in the fourth quarter of 2001, there was a drop of 18 percent in the number of passengers compared with the same time period in 2000. Many still avoid air travel. We thus thought it appropriate to again calculate the risks involved in flying and driving, taking into account the latest statistics, including the tragic deaths of the passengers on those four hijacked planes.