This contribution presents an approach for the optimal scheduling of maintenance activities of metallic structures prone to develop fatigue cracks. The crack propagation phenomenon is addressed using a fracture mechanics approach. The uncertainties in crack propagation and in inspection activities are modeled explicitly using probabilistic tools. Thus, the problem of scheduling of maintenance activities is addressed within the framework of reliability-based optimization (RBO); therefore, it is possible to minimize the cost of inspection, repair and eventual failure while explicitly accounting for the effects of uncertainties. For solving the underlying RBO problem, an efficient method recently developed by the authors is applied. Key features of this method are the identification of descent-feasible directions and the implementation of a line search strategy, in combination with an efficient approach for estimating reliability sensitivity. An application example addressing the practical implementation of the proposed approach is presented.