The sensitivity of primary knock-on atom (PKA) spectra and displacement per atom (dpa) cross sections to different secondary neutron energy and angular distributions and “in-group” weighting schemes is investigated. It is shown that the sensitivity of the PKA spectra and dpa cross sections for the (n, n′ unresolved) and (n, 2n) reactions in iron to different angular distributions and the same secondary neutron spectrum is reasonably large (∼15%). For grossly different secondary neutron spectra and the same angular distribution, the change in the dpa cross section is smaller than one would initially expect. It is also shown that for aluminum, the sensitivity of dpa cross sections to different in-group weighting schemes is, for the most part, small.