  We investigate the nature (Dirac vs. Majorana) and size of left-handed
neutrino masses in a supersymmetric five-dimensional model compactified in the
interval [0,\pi R], where quarks and leptons are localized on the boundaries
while the gauge and Higgs sectors propagate in the bulk of the fifth dimension.
Supersymmetry is broken by Scherk-Schwarz boundary conditions and electroweak
breaking proceeds through radiative corrections. Right-handed neutrinos
propagate in the bulk and have a general five-dimensional mass M, which
localizes the zero modes towards one of the boundaries, and arbitrary boundary
terms. We have found that for generic boundary terms left-handed neutrinos have
Majorana masses. However for specific boundary configurations left-handed
neutrinos are Dirac fermions as the theory possesses a conserved global U(1)
symmetry which prevents violation of lepton number. The size of neutrino masses
depends on the localization of the zero-modes of right-handed neutrinos and/or
the size of the five-dimensional neutrino Yukawa couplings. Left-handed
neutrinos in the sub-eV range require either MR~10 or Yukawa couplings
~10^{-3}R, which make the five-dimensional theory perturbative up to its
natural cutoff.
