A parallel CFD code capable of simulating flow within moving boundaries has been coupled to a beam element structural dynamics code. The coupled codes are used to simulate fluid- structure interaction for a class of applications involving long and slender structures, e.g. suspension bridges and offshore risers. Due to the difference in size and dimensionality of the 3D CFD problem on one side, and the essentially 1D structure problem on the other side, the bulk of the computations are carried out in the CFD code. The parallel efficiency of the coupled codes thus rest on the paralll performance of the CFD code, and on minimizing the amount of communication between the two codes. The CFD code uses implicit time stepping, and is parallelized by a multiblock technique based on a block-Jacobi iteration together with coarse grid correction. To reduce the amount of communication between the CFD code and the structure code, the mesh movement algorithm is split into two parts, where the most computationally intensive part is carried out in parallel within the CFD code. The resulting coupled system has a high parallel efficiency even if the structure code runs on a workstation and the CFD code runs on a parallel supercomputer provided that the size of the CFD problem is sufficiently large.