  In models where the Standard Model spectrum is localized on a brane embedded
in a higher dimensional spacetime, we discuss the lepton number violation
induced by the emission of right-handed neutrinos from the brane. We show that
quite generically the presence of the right-handed neutrinos in the bulk leads
to rapid lepton number violating processes which above the electroweak scale
would wash away any prior lepton or baryon asymmetry. In order to preserve the
lepton asymmetry, the brane-bulk couplings for at least one lepton flavor must
be extremely suppressed. We show that this has a natural interpretation in the
brane world.
