This study concentrates on the efficiency of numerous ground motion intensity measures (IMs) to be used in estimating the response of seismic-isolated bridges (SIBs). Efficiency of commonly used IMs was investigated through their correlation with maximum isolator displacement (MID) obtained from nonlinear dynamic analyses. Two sets of ground motions (GMs), classified as ordinary and pulse-like, were used in nonlinear dynamic analyses of SIBs. In the analyses, varying isolation parameters, such as the isolation period, T, and the characteristic strength of the isolator, Q(d)/W, were studied. Sensitivity to varying T and Q(d)/W and the effect of ground motion type on the correlation of IMs with MID of SIBs were examined. To improve the correlation of existing IMs, modified IMs were proposed. The results revealed that the isolation period has a pronounced effect on the correlation of IMs with MID of SIBs, especially for pulse-like GMs. Among the investigated IMs, modified velocity spectrum intensity appears to have the strongest correlation with MID of SIBs for a wide range of isolation parameters and ground motion type. DOI: 10.1061/(ASCE)BE.1943-5592.0000340. (C) 2013 American Society of Civil Engineers.