A new approach to simulate fluorescence photons produced in extensive air showers is described. A Monte Carlo program based on CORSIKA produces the fluorescence photons for each charged particle in the development of the shower. This method results in a full three-dimensional simulation of the particles in a shower and of the fluorescence light generated in the atmosphere. The photons produced by this program are tracked down to a telescope and the simulation of a particular detector is applied. The differences between this method and one-dimensional approaches are quantitatively determined as a function of the distance between the telescope and the shower core. As a particular application, the maximum distance at which the Auger fluorescence telescope might be able to measure the lateral distribution of a shower is determined as a function of energy.