Abstract: This paper presents a practical optimum design solution of prismatic simply supported prestressed concrete girders that are subjected to uniformly distributed static loads. The process is formulated as a nonlinear optimization model while assuming linear elastic behavior and employing the working stresses method. The process produces the optimum values of two design variables, namely the cross-sectional dimensions and the prestressing force. Those optimized values are computed to satisfy either a minimum weight or a minimum cost objective function. To solve the nonlinear programming models, a program named Nonlinear Programming Prestressed Concrete Optimizer (NLPRECO) was coded in MATLAB® programming environment. Some illustrative design problems were solved using NLPRECO, and their results are demonstrated herein. Sensitivity analysis of the optimized design variables, to variations in design parameters, was also investigated, and the results are presented. Results show substantial improvement over the regular un-optimized solutions and moderate improvement over linear programming optimization solutions.