The response function of a 12.5 cm diameter NE213 scintillator detector has been measured over neutron energies ranging from 4.9 to 16.6 MeV. Beams of monoenergetic neutrons were produced using the 2H(d, n) 3He reaction. The response function is about 12% lower than previously reported values for a similar detector obtained using a continuous spectrum of neutrons from a 252Cf fission source. However, the present response function agrees with portions of data sets obtained in published work that used monoenergetic neutron source reactions.