  The staggered magnetization of the Heisenberg antiferromagnet in two
dimensions can be systematically approximated by a 1/N expansion. Cancellation
between self energy diagrams leads to a Luttinger-like theorem for the ground
state. We prove (for a smooth enough self energy) that the long range order of
mean field theory ($N$=$\infty$) survives corrections to all orders of 1/N.
Divergences of this series provides a new route to the disordered phases of
quantum antiferromagnets.
