With D. Ben-Zvi.  ``Cusps and D-modules,'',
J. Amer. Math. Soc. 17 (2004), 155--179.
We prove that categories of D-modules on certain singular varieties ("cusp singularities") are equivalent to categories of D-modules on smooth varieties, resolving conjectures of Hart-Smith and Berest-Etingof-Ginzburg.