A manganese sulphate bath technique has been used to make an accurate measurement of the 9Be (n, 2n) cross section averaged over a pure 252Cf spontaneous fission-neutron spectrum. Monte Carlo calculations were performed to correct precisely for spectrum distortion due to elastic scattering in the beryllium. Corrections were also made for all other competing reactions of importance. The result obtained, 144 ± 6 mb, is in good agreement with the value of 150 mb calculated from an excitation curve based on the latest available differential data.