The Monte Carlo method is used to calculate the leakage neutron spectrum of the White Sands Missile Range Fast Burst Reactor. The leakage spectrum is then used as the source spectrum for further calculations, which are directly compared to experimental data. The calculated spectrum differs somewhat from the experimentally measured shape, particularly in the 3- to 6-MeV region. The calculated spectra have a higher spectral index (fluence > 10 keV/fluence > 3 MeV) than the experimentally determined spectra. Generally, the two methods of determining the spectra appear to be in reasonable agreement.