The conditions for higher-mode cutoff in dielectric wave-guides of elliptical cross-section are derived. A table of values of the waveguide parameter V at higher-mode cutoff is given together with a curve showing the variation with ellipticity from circular to slab guide. The conditions for higher-mode cutoff in dielectric wave-guides of elliptical cross-section are derived. A table of values of the waveguide parameter V at higher-mode cutoff is given together with a curve showing the variation with ellipticity from circular to slab guide.