Although 4-substituted pyridinium derivatives studied so far form the 2:1 complexes with cadmium iodide, an exceptional 1:1 complex was found for 1-methyl-4-carbamoylpyridinium iodide. Its X-ray crystallographic analysis revealed that its inorganic portion has a unique structure with corner-sharing one-dimensional tetrahedral chains of (CdI3-)(n).