The structures of N-(2-chlorophenyl)-4-hydroxy-2-methyl-2H-1, 2-benzothiazine-3- carboxamide 1, 1-dioxide and N-(4-chlorophenyl)-4-hydroxy-2-methyl-2H-1, 2- benzothiazine-3-carboxamide 1, 1-dioxide, both C16H13ClN2O4S, are stabilized by extensive intramolecular hydrogen bonds. The 4-chloro derivative forms dimeric pairs of molecules lying about inversion centres as a result of intermolecular N—H⋯ O hydrogen ...