The paper describes risk-informed decision support for assessing the costs and benefits of Counter-Terrorism (CT) protective measures for infrastructure. As such, a cost-benefit assessment needs to consider risk reduction, threat probability, and fatality and damage cost estimates. Cost-benefit assessments are conducted for three items of infrastructure using representative cost and vulnerability data. The illustrative examples showed under what combination of risk reduction, threat probability, and fatality and damage costs the CT protective measures would be cost-effective for building, bridge and aviation infrastructure. It was found that unless terrorist threat probabilities are high, then typical CT protective measures are not cost-effective. Opportunity costs associated can be considerable which makes CT protective measures even less cost-effective. The threat likelihood for bridges is considerably less than for buildings. With the possible exception of ‘key assets’, most individual items of infrastructure are likely to be not ‘critical’ to the nation or the economy and so in many cases not cost-effective to protect against terrorism.