Crystal structures of a new polymorph of N,N'-(p-phenylene)bis(benzenesulfonamide) (C18H16N2O4S2) and of two inclusion compounds with acetone [(CH3)2CO] and dimethyl sulfoxide [2(CH3)2SO], respectively, have been determined at 150 K. For a more reliable comparison, the structure of the already known polymorph of N,N'-di(benzenesulfonyl)-p-phenylenediamine has been redetermined under identical conditions. In addition, the phase transformation behavior has been examined by differential scanning calorimetry and the crystallization conditions of both polymorphs including their formation by weathering of the inclusion compounds were investigated.