In Mariusz Wodzicki's paper "Cyclic homology of differential operators," the following result is mentioned: for $D\_M$ the algebra of differential operators on a smooth manifold $M$ we have that $HH\_n(D\_M) \cong H\_{DR}^{2m-n}(M)$ where $m=\dim M$. I'm having trouble finding a reference for the Hochschild Cohomology of $D\_M$. Does anyone know of a paper with the result?