  We define and present some proprieties of the M\"obius inversion of surfaces
in the Minkowski 3-space. We prove that the M\"obius inversion preserves the
lines of principal curvature and the locus of points where the metric is
degenerate, but it does not preserve the parabolic set. For ovaloids, we show
that it is possible to translate the surface so that the inversion remains an
ovaloid.
