The structure of a new polymorph of the title compound, C(10)H(13)ClN(2)O(3)S, known as the antidiabetic drug chlorpropamide, is monoclinic, in contrast with the two previously described orthorhombic alpha- and beta-forms. The molecules in the gamma-polymorph are linked into bands by hydrogen bonds similar to those in the alpha-polymorph. The conformation of the molecules in the gamma-form is close to that in the beta-polymorph.