A detailed evaluation of the R matrix resonance parameters describing the interaction of neutrons with 235U has been performed up to 500 eV using the most recent high-resolution measurements of the 235U neutron cross sections. The availability of 235U spin-separated neutron cross-section data, in conjunction with the use of the Δ3 statistics of Metha and Dyson, has made possible a detailed study of the statistical distribution of the resonance parameters and their average values. The present R matrix resonance parameters have been converted into equivalent sets of Adler-Adler parameters and multipole momentum space expansion parameters. Extensive validation of this evaluation has been performed by comparing self-shielded fission rates computed with these R matrix parameters with the measurements of Czirr; a test of the ENDF/B unresolved resonance formalism for the calculation of 235U self-shielding factors is also presented.