  We present a version of the Matsuki correspondence for the affine
Grassmannian $Gr=G(C((t)))/G(C[[t]])$ of a connected reductive complex
algebraic group $G$. The main statement is an anti-isomorphism between the
orbit posets of two subgroups of $G(C((t)))$ acting on $Gr$. The first is the
polynomial loop group $LG_R$ of a real form $G_R$ of $G$; the second is the
loop group $K(C((t)))$ of the complexification $K$ of a maximal compact
subgroup $K_c$ of $G_R$. The orbit poset itself turns out to be simple to
describe.
