We calculate the one-loop radiative corrections to gauge-boson masses in SU(2${)}_{\mathrm{L}}$\ifmmode\times\else\texttimes\fi{}U(1${)}_{\mathrm{Y}}$ electroweak gauge models with an extended Higgs sector in an on-shell renormalization scheme. Current gauge-boson mass measurements restrict certain Higgs-boson masses to lie below the unitarity bound. Future precise measurements of the Z-boson mass can significantly reduce this limit. We also compare our results to previous calculations for the shift in the \ensuremath{\rho} parameter.