  We have performed elastic diffuse neutron scattering studies on the relaxor
Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$ (PMN). The measured intensity distribution near a
(100) Bragg peak in the (hk0) scattering plane assumes the shape of a butterfly
with extended intensity in the (110) and (1$\bar{1}$0) directions. The
temperature dependence of the diffuse scattering shows that both the size of
the polar nanoregions (PNR) and the integrated diffuse intensity increase with
cooling even for temperatures below the Curie temperature $T_C \sim 213$ K.
