Perturbative unitarity for W_L⁺ W_L^- \to W_L⁺ W_L^- scattering is discussed within the Randall--Sundrum theory with two 3-branes. It is shown that the exchange of massive 4D Kaluza--Klein gravitons leads to amplitudes growing linearly with the CM energy squared. If the curvature, m₀, of the metric is too small, the gravitational contributions lead to a violation of unitarity. However, m₀ must be small enough relative to the 5D Planck mass, M_Pl5, to avoid quantum gravitational effects. As a result, we find that there is only a small range of m₀/{M_Pl} for which the model is consistent. The width of the window is determined by the size of the 4D cutoff of the theory. The extension of the Randall--Sundrum scenario to include curvature-Higgs mixing is also considered and limits on the mixing parameter are determined.

PACS numbers: 11.10.Kk, 04.50.+h, 11.15.--q, 11.80.Et