Could healthcare costs be reined in by improving access to preventive care? It's an idea that appeals to policy makers and many public health experts, but the evidence for it is surprisingly hard to pin down. Of course, preventing diseases is better than waiting for them to occur and then treating them. But there are questions about which diseases can actually be prevented, how effective preventive measures might be, and what they would cost. We put some of these questions to Dana Goldman, director of the Schaeffer Center for Health Policy and Economics at the University of Southern California and founding editor of the Forum for Health Economics and Policy.