The 19F(n,2n)18F cross section is measured at neutron energies of 18, 21, 23, 25, and 27 MeV. Nearly monoenergetic neutrons bombarded Teflon [(C2F4)n], zirconium, and gold samples. The 19F(n,2n)I8F cross-section values are determined relative to natZr(n,xn)89Zr and 197Au(n,2n)196Au from measurements of the 18F, 89Zr, and 196Au activities. Results are in agreement with previous measurements below 20 MeV and extend the usefulness of this reaction to 27 MeV.