This paper is concerned with optimum design and sensitivity of retaining structures. The optimum design formulation in terms of a constrained nonlinear programming problem, is given for reinforced concrete-cantilever retaining walls. The objective function may be chosen as the cost or weight of the wall. The solution is carried out by a specially prepared computer program (RETOPT). Illustrative problems are solved, and their results are presented and discussed. The formulation allows for a detailed sensitivity analysis to be made for selected design parameters, also depicted with numerical examples.