The cumulative increase in expenditures on US domestic homeland security over the decade since 9/11 exceeds one trillion dollars. It is clearly time to examine these massive expenditures applying risk assessment and cost-benefit approaches that have been standard for decades. Thus far, officials do not seem to have done so and have engaged in various forms of probability neglect by focusing on worst case scenarios; adding, rather than multiplying, the probabilities; assessing relative, rather than absolute, risk; and inflating terrorist capacities and the importance of potential terrorist targets. We find that enhanced expenditures have been excessive: to be deemed cost-effective in analyses that substantially bias the consideration toward the opposite conclusion, they would have to deter, prevent, foil, or protect against 1,667 otherwise successful Times-Square type attacks per year, or more than four per day. Although there are emotional and political pressures on the terrorism issue, this does not relieve politicians and bureaucrats of the fundamental responsibility of informing the public of the limited risk that terrorism presents and of seeking to expend funds wisely. Moreover, political concerns may be over-wrought: restrained reaction has often proved to be entirely acceptable politically.