A process of making an aromatase inhibitor of formula (I) wherein each of R<;SUP>;1<;/SUP>;, R<;SUP>;2<;/SUP>;, R<;SUP>;3<;/SUP>;, and R<;SUP>;4<;/SUP>;, independently, is hydrogen, halogen, or C<;SUB>;1<;/SUB>;-C<;SUB>;6 <;/SUB>;alkyl, comprising reacting a compound of formula (II) with an acid in the presence of a suitable solvent. A new crystalline form of exemestane and is also disclosed.