The neutron flux generated at the main proton beam stop of the Los Alamos Clinton P. Anderson Meson Physics Facility (LAMPF) has unique properties of interest to materials radiation studies. Two of these properties—the total neutron flux and the neutron energy spectrum—were studied. The total neutron flux at the LAMPF radiation effects facility has been calculated by Monte Carlo techniques and measured by foil activation methods. The measurement compares well with the calculation and gives a total flux at the measurement position of 2 × 1011 n. mm−2 . s−1 at 1 mA of proton beam current. Later calculations at other locations show a flux of 1 × 1012 n . mm−2 . s−1.