This paper presents the stochastic seismic response analysis of offshore wind turbines subjected to multi-support seismic excitation by using a three-dimensional numerical finite element model considering viscous boundaries. The seawater-offshore wind turbine-soil interaction system is modelled by the Lagrangian (displacement-based) fluid and solid-quadrilateral-isoparametric finite elements. The random seismic excitation is described by the filtered white noise model and applied to each support point of the three-dimensional finite element model of the coupled interaction system. The research conducts a parametric study to estimate the effects of variable seawater level, different foundation soil types and support site conditions on the stochastic behaviour of the offshore wind turbine coupled interaction system. The finite element model of coupled interaction system was also analyzed to examine the effect of the surrounding ice sheet on the stochastic response of the coupled system with and without ice sheet. The results obtained for different cases are compared with each other. Copyright (c) 2010 John Wiley & Sons, Ltd.