Abstract The crystal structure of dithiomalonediamide (H2C(CS-NH2)2) has been determined. The compound crystallizes in the orthorhombic space group P2nn, No. 34, with a = 4.354(3), b = 7.940(5) and c = 8.458(5) Å. The molecules are connected by S ··· H bridges to form helices along the crystallographic a axes.