Risk aspects of planning and design of engineering works in Mexico are usually considered into the mitigation and development plans only in a subjective and qualitative form. This practice does not produce the minimum costs in the long term. In order to optimally allocate limited funds used for mitigation purposes, a careful, systematic and objective estimation of the failure consequences as well as the underlying risk is required. Also, mitigation policies for several regions in Mexico and different hazard types are not risk-consistent. In this paper a criterion to calculate cost/benefit ratios in terms of the expected number of fatalities, the expected losses and the investment made on structural safety is proposed. The criterion may be used to appraise the risk on engineering works and to compare the consistency of risk mitigation expenditures made by national highway agencies with the cost/benefit involved on the increment of structural safety for buildings. These concepts may be considered to generate an effective risk management for optimal policies for life and property protection. This formulation is applied to the specific case of buildings under seismic exposure in Mexico City and expected life-cycle cost functions are developed for typical costs and practices.