In this paper, stochastic responses of seismically isolated highway bridges with friction pendulum systems subjected to spatially varying earthquake ground motions are investigated. The spatially varying earthquake ground motion model includes incoherence, wave-passage and site-response effects. The incoherence effect is examined by considering the Harichandran and Vanmarcke coherency model. The effect of the wave-passage is investigated by using various wave velocities. Homogeneous soft, medium and firm soil types are selected for considering the site-response effect where the bridge supports are constructed. The ground motion is described by filtered white noise and applied to each support point. Due to the presence of friction on the concave surface of the frictional pendulum system, the equation of motion is non-linear. The non-linear equation of motion is solved by using equivalent linearization techniques of non-linear stochastic analyses. The frictional pendulum system's behaviour is programmed in the FORTRAN language by the authors and incorporated into the program SVEM. Solutions obtained from the stochastic analyses of non-isolated and isolated bridges to spatially varying earthquake ground motions are compared with each other for the special cases of the ground motion model. It is concluded that friction pendulum systems have important effects on the stochastic responses of bridges to spatially varying earthquake ground motions. (c) 2005 Elsevier Ltd. All rights reserved.