A series of indole- and carbazole-substituted pyridinium iodide salts has been synthesized and characterized. X-ray analysis revealed that the iodide salt of the indole-substituted cation (E)-4-(1H-indol-3-ylvinyl)-N-methylpyridinium (IMPE(+)), C(16)H(15)N(2)(+) x I(-), (I), has two polymorphic modifications, (Ia) and (Ib), and a hemihydrate structure, C(16)H(15)N(2)(+) x I(-) x 0.5H(2)O, (II). Until now, only one crystal modification has been identified for the (E)-4-(9-ethyl-9H-carbazol-3-ylvinyl)-N-methylpyridinium (ECMPE(+)) iodide salt, C(22)H(21)N(2)(+) x I(-), (III). Crystals of (Ia) and (Ib) comprise stacks of antiparallel cations with iodide anions located in the channels between the stacks. Due to the presence of the water molecules, the packing in (II) is quite different to that found in (Ia) and (Ib), and positional disorder involving a statistical superposition of two rotamers of IMPE(+), with different orientations of the indole fragment, was found. Crystals of (III) contain two independent ECMPE(+) rotamers with different orientations of their carbazole substituents. The cations are packed in stacks, with the iodide anions located in the channels between the stacks. In (III), the iodide was found to be disordered over two sites, with occupancies of 0.83 and 0.17.