ABSTRACT: Current trends in the use of improvised explosive devices against civilian buildings pose a significant challenge to the professionals entrusted with the design of protective measures for blast risk mitigation. A rigorous approach to this problem requires a probabilistic assessment of risk, in order to weigh costs and benefits of potential interventions; however, current design standards for blast protection are still based on deterministic notions of threat, hazard, load demand and capacity, and cost—which do not acknowledge the inherent uncertainty associated with the variables defining a structural system. To demonstrate its significance, a risk assessment methodology is applied herein to the problem of a masonry wall under blast overpressure: Monte Carlo simulations are carried out to determine the wall failure probabilities and cost of repair/replacement. The results are expected to foster the future development of risk-based guidelines for the design of blast resistant masonry buildings.