  We propose gauge theory/gravity duality involving conformal theories based on
U(N+k|k) gauge groups. We show that to all orders in 1/N these non-unitary
theories based on supergroups are indistinguishable from the corresponding
unitary theories where the gauge group is replaced by U(N). This leads to
non-unitary gravity duals which to all orders in 1/N are indistinguishable from
their unitary cousins. They are distinguished by operators whose correlation
functions differ by O(exp(-aN)). The celebrated type IIB on AdS^5 x S^5 and
M-theory on AdS^4 x S^7 fall in this class and thus seem to also admit
non-unitary non-perturbative completions. It is tempting to conjecture that
this setup may provide a non-unitary model for black hole evaporation.
