Transition to turbulence induced by unstable stationary crossflow vortices in a three-dimensional laminar boundary layer on a Mach 1.5, 25 deg swept wing is investigated with the nonlinear compressible Parabolized Stability Equations (PSE). The wing has 3m span, lm chord, and is untwisted and untapered. Body-fitted coordinates are used to account for all curvature effects of the wing's NACA 64A010 airfoil.The stationary crossflow vortices interact to produce spanwise-periodic harmonics as well as a steady, spanwise-invariant distortion of the underlying laminar flow. The streamwise growth and evolution of all the disturbances is computed for different initial amplitudes of the primary crossflow vortices. For the few initial amplitudes investigated, all the disturbances are found to grow to the point where the mean flow profiles exhibit regions of reversed flow. Beyond this point, the streamwise marching solution is no longer valid. Just before this occurs, however, the mean flow distortion is sufficiently large that the mean wall shear stress suddenly and rapidly increases above the laminar value. At these large amplitudes, the disturbed flow becomes subject to high frequency inviscid instabilities and transition to turbulence should soon ensue.