The phasor measurement technology has made it possible the monitoring and control of wide-area power systems. In this study, a new genetic algorithm based method for optimal placement of phasor measurement units (PMUs) considering observability and security issues is proposed. The idea is to allocate the least number of PMUs while providing the most redundant set of measurements. This allocation philosophy ensures reliability in the state estimation process. Moreover, the allocation method also takes into account security issues, by preserving the system's observability in case of loss of PMUs. In particular, the loss of a single PMU [(n - 1) criterion] is considered. The proposed method was tested on IEEE standard test systems and the results are discussed and evaluated.101 270280