For the first time full next-to-leading-order electroweak corrections to off-shell vector-boson scattering are presented. The computation features the complete matrix elements, including all non-resonant and off-shell contributions, to the electroweak process \(\mathrm{p} \mathrm{p} \to \mu^+ \nu_\mu \mathrm{e}^+ \nu_{\mathrm{e}} \mathrm{j} \mathrm{j}\). It is fully differential, and event selections are applied to the final states such that the predictions can be directly compared to experimental measurements. The corrections are surprisingly large, reaching -16% for the fiducial cross section and up to -40% in the tails of distributions. These large corrections are due to enhanced logarithms in the bosonic virtual corrections.