The Standard-Model Higgs boson with mass MH ≫ 2MZ decays almost exclusively to pairs of W and Z bosons. We calculate the dominant two-loop corrections, of O(GFM 4 H), to the partial widths of these decays. In the on-mass-shell renormalization scheme, the correction factor is found to be 1 + 14.6%(MH/TeV) 2 + 16.9%(MH/TeV) 4, where the second term is the one-loop correction. We give full analyti...