  The predictions of the atmospheric nu event rates are affected by significant
uncertainties, however the evidence for the `disappearance' of nu_mu's and
antinu_mu's obtained by SK and other underground detectors is robust and cannot
be accounted in the framework of the minimum standard model without assuming
very large ad hoc experimental systematic effects. The existence of `new
physics' beyond the standard model is therefore close to be established;
neutrino oscillations provide a very good fit to all data. The theoretical
uncertainties do have an important role in the detailed interpretation of the
data, and in the estimate of oscillation parameters.
