  This paper surveys our current knowledge of the hard X-ray emission
properties of old accreting neutron stars in low mass X-ray binaries. Hard
X-ray components extending up to energies of a few hundred keV have been
clearly detected in sources of both the Atoll and Z classes. The presence and
characteristics of these hard components are discussed in relation to source
properties and state. An overall anticorrelation between the fraction
luminosity in hard X-rays and mass accretion rate is apparent over different
sources spanning a large range of luminosities as well as individual source
undergoing state changes. Evidence for a second, yet unknown, parameter
controlling the hard X-ray emission is emerging. We draw a parallel with the
spectral properties of X-ray binaries hosting a stellar mass accreting black
hole, and conclude that, at a merely phenomenological level, there appears to
be a close analogy between the spectral properties of black hole candidates in
their high and intermediate states and Z-sources. We briefly mention models
that have been proposed for the hard X-ray emission of neutron star low mass
X-ray binaries and comment on perspectives in the INTEGRAL era.
