Abstarct: In traditional integrated structural optimization, the common procedure is to carry a structural topology optimization followed by shape optimization where the topology of the structure does not vary. In this research work a combined shape and topology optimization method for finding the optimum shape of the mid-plane of shell structures together with the optimum layout of the surface stiffeners is proposed. The solution is baxsed on a finite element discretization of the design domain. The material within each element is modeled by artificial materials with rectangular microscale voids. The geometric parameters of the microscale voids of the artificial material are taken as design variables of the topology optimization loop of optimization procedure. The geometry of the shell structures are generated by NURBS surfaces and the control points of the surface are considered as design variables in the shape optimization loop. The optimization problem in each loop is solved by the method of moving asymptotes (MMA) and design sensitivity analysis. The proposed approach is applied to a few examples and the obtained results are presented.