  We discuss baryon and lepton violation in the context of a simple
5-dimensional grand unified model, based on the orbifold S^1/(Z_2 x Z_2').
While gauge and Higgs degrees of freedom live in the bulk, matter is located on
the boundaries of the space-time. We show that proton decay is naturally
suppressed or even forbidden by suitable implementations of the parity
symmetries in the matter sector. The corresponding mechanism does not affect
the SU(5) description of fermion masses also including neutrinos.
