The transmission of a Gaussian beam through a Fabry-Perot interferometer (FPI) has been investigated. The equation for the electric field of the transmitted beam was derived and then the transmitted irradiance I(t) was numerically calculated for different selected parameters of both the FPI and the beam. The results show that the energy profile of the transmitted beam has been distorted to different degrees depending on the various parameters of the Gaussian beam and the FPI. Moreover the results show that the positions of the peaks of the transmitted beam are shifted, especially for intermediate waists for which the arctan term is nonlinear. The results also show that for nonnormal incidence successive transmitted beams are spatially separated and are not interfering appreciably with each other.