Mixed crystals of 1-(4-chlorophenylsulfonyl)-2,5-dimethyl-1H-benzimidazole and 1-(4-chlorophenylsulfonyl)-2,6-dimethyl-1H-benzimidazole (ratio 0.707:0.293; two molecules in the asymmetric unit), 0.707C15H13ClN2O2S·0.293C15H13ClN2O2S, (I), and of 2-n-butyl-1-(4-tert-butylphenylsulfonyl)-5-chloro-1H-benzimidazole and 2-n-butyl-1-(4-tert-butylphenylsulfonyl)-6-chloro-1H-benzimidazole [ratio 0.731 (2):0.269 (2); one molecule in the asymmetric unit], 0.731C21H25ClN2O2S·0.269C21H25ClN2O2S, (II), were obtained from the arylsulfonylation reaction of the corresponding 2-alkylbenzimidazoles. In addition, two products were obtained from the reaction of 2-n-butyl-5-chloro-1H-benzimidazole with 4-methylbenzenesulfonyl chloride. These reaction products were separated by column chromatography and the crystal structure of one of the products, 2-n-butyl-5-chloro-1-(4-methylphenylsulfonyl)-1H-benzimidazole (one molecule in the asymmetric unit), C18H19ClN2O2S, (III), was determined. In the crystal structures of (I)–(III), there is a difference in the arrangement of the planar benzimidazole and arylsulfonyl fragments. The formation of weak C—H...O hydrogen-bonding interactions is characteristic of all three crystal structures.