A two-dimensional method of moments solution technique for the simulation of electrically large structures is presented. This technique is based on a boundary integral equation description, and was designed to keep CPU time and memory requirements within acceptable limits even for problems of several thousands of unknowns. This is achieved through an optimized calculation of the interaction integrals leading to the moment method interaction matrix and through a so-called impedance matrix transformation of this matrix to a sparse form. The resulting sparse system of linear equations is efficiently solved using a conjugate gradient algorithm. The entire solution technique is applied to the simulation of indoor wave propagation problems and is illustrated by two examples.