Fragility curves are useful tools for showing the probability of structural damage due to earthquakes as a function of ground motion indices. The aim of this study is to develop the fragility curves for mid-rise R/C frame buildings in Istanbul, which have been designed according to the 1975 version of the Turkish seismic design code, based on numerical simulation with respect to the number of stories of the buildings. Sample 3, 5 and 7 story buildings were designed according to the Turkish seismic design code. Incremental dynamic analyses were performed for those sample buildings using twelve artificial ground motions to determine the yielding and collapse capacity of each sample building. Based on those capacities, fragility curves were developed in terms of elastic pseudo spectral acceleration, peak ground acceleration (PGA) and elastic spectral displacement for yielding and collapse damage levels with lognormal distribution assumption. To investigate the effect due to the number of stories of the building on fragility parameters, regression analysis has been carried out between fragility parameters and the number of stories of the building. It was observed that fragility parameters change significantly due to the number of stories of the building. Finally, using constructed fragility curves and statistical methods, the maximum allowable inter-story drift ratio and spectral displacement values that satisfy the "immediate occupancy" and "collapse prevention" performance level requirements were estimated. (c) 2006 Published by Elsevier Ltd.