Collisions between adjacent structures due to insufficient separation gaps have been witnessed in almost every major earthquake since the 1960's. Although many analytical, numerical and experimental studies have been conducted into the pounding phenomenon, the number of those which take into account the effects of the underlying soil mass on the dynamic response of the colliding structures are almost negligible. The present study incorporates the effects of soil flexibility on the inelastic dynamic response of a particular case of adjacent 12- and 6-storey reinforced concrete moment-resisting frames. The time- history response of this system (linear soil behaviour and nonlinear structural response) subjected to actual earthquake records is evaluated by means of the structural analysis software RUAUMOKO developed at the University of Canterbury. A simple mass-spring-dashpot model is used to represent the frequency independent dynamic soil properties. Impacts at storey levels only are considered. This study highlights serious inconsistencies in the assumptions of previous pounding studies, which neglect the effects of soil flexibility. Also, the pounding response of the adjacent structures is found to be highly sensitive to the characteristics and direction of the seismic excitation.