  We consider the proton structure corrections to hydrogen ground-state
hyperfine structure, focusing on a state-of-the-art evaluation of the inelastic
nucleon corrections--the polarizability corrections--using analytic fits to the
most recent data. We find a value for the fractional correction Delta_{pol} of
1.3 \pm 0.3 ppm. This is 1--2 ppm smaller than the value of Delta_{pol}$ one
would deduce using hyperfine splitting data and elastic proton structure
corrections obtained from modern form factor fits. In addition, we discuss the
derivations of the relevant formulas, paying attention to lepton mass effects
and to questions surrounding the use of unsubtracted dispersion relations.
