For architectural reasons or restrictions imposed by local laws, many multistory buildings are designed with setbacks. ln this paper, the behavior of high rise symmetric and unsymmetric setback structures under the effect of ground motion excitation is investigated using time history dynamic analysis. Several setback sizes and levels have been considered. Effects of setback parameters on key response values of the Structures were examined. These response values include fundamental translational periods of vibration, torsional periods of vibration, setback level displacement, top story displacement, base shear, base torsional moment and maximum input earthquake energy. Results indicate the feasibility of obtaining satisfactory code formulas to relate key response parameters of a setback structure to the corresponding uniform one.