Since the support structure of an offshore wind turbine has to withstand severe environmental loads such as wind, wave, andseismic loads during its entire service life, the need for a robust and reliable design increases, along with the need for a cost effective design. Inaddition, a robust and reliable support structure contributes to the high availability of a wind turbine and low maintenance costs. From this pointof view, this paper presents a design process that includes design optimization and reliability analysis. First, the jacket structure of the NREL5-MW offshore wind turbine is optimized to minimize the weight and stresses, while satisfying the design requirements. Second, the reliability ofthe optimum design is evaluated and compared with that of the initial design. Although the present study results in a new optimum shape for ajacket support structure with reduced weight and increased reliability, the authors suggest that the optimum design has to be accompanied by areliability analysis during the design process, as well as reliability based design optimization if needed.