  Assuming that right-handed neutrinos exist and propagate in some large extra
dimensions, we attempt to give a comprehensive description of the phenomenology
of neutrino oscillations. A few alternative explanations of the atmospheric
neutrino anomaly emerge, different from the standard nuMu --> nuTau or nuMu -->
nuSterile interpretations. Constraints from nucleosynthesis and supernova 1987a
are discussed. The constraints from SN1987a indicates a maximum radius of any
extra dimension of about 1 Angstrom.
