Evolutionary multiobjective optimization is employed for designing the geometric configurations of winglets adapted to a base wing. Seven decision variables are employed for the winglet parameterization, and the wing-winglet transition region is modeled using Bezier surfaces. A case study is presented to illustrate the application of this technique to the design of wingtip devices. The optimization model includes two objectives: the ratio of drag-lift coefficients, and the wing root bending moment coefficient. The solutions obtained are discussed, and a Monte Carlo sensitivity analysis is performed to test the robustness of the results to uncertainties in the variables. Finally, a winglet geometry is suggested to be retrofitted to the base wing, providing an increased lift to drag ratio at the expense of increasing the root bending moment of the wing.