A reliability analysis is usually required to carry out design optimization of large structural systems to incorporate the uncertainties on the parameters such as material properties, external loads, manufacturing condition, etc. This procedure is called Reliability Based Design Optimization (RBDO), and requires a structural analysis program, a reliability analysis and optimization tools to couple effectively. In this paper, an integrated framework is proposed to implement the RBDO of the offshore towers. It has two distinct approaches to evaluate the probabilistic constraints; namely Reliability-Index based Approach (RIA) and Performance Measure Approach (PMA). The proposed framework also suggests Sequential Quadratic Programming (SQP) and Differential Evolution (DE) as optimization methods. Examples of monopod, tripod, and jacket towers under the reliability constraints based on limit states of the critical stress, buckling, and the natural frequency are presented to demonstrate the applicability of the implemented algorithm to realistic structural systems. (C) 2010 Elsevier Ltd. All rights reserved.