  We microscopically derive the Ginzburg-Landau free energy functional for a
noncentrosymmetric superconductor with a large spin-orbit splitting of the
electron bands, in the presence of nonmagnetic impurities. The critical
temperature is found to be suppressed by disorder, both for conventional and
unconventional pairing, in the latter case according to the universal
Abrikosov-Gor'kov function. The impurity effect on the upper critical field
turns out to be nonuniversal, determined by the pairing symmetry and the band
structure. In a BCS-like model, Tc is not affected, while Hc2 increases with
disorder. For unconventional pairing, both Tc and Hc2 are suppressed by
disorder.
