The isolation of stable carbenes of the Arduengo (1a) and Wanzlick (2a) type has prompted us to look for stable nitrenium ions of the related structural type 1-methyl-3-(4-nitrophenyl)-1,2,3 triazolium perchlorate (6). The title compound (C-9 H-11 Cl N-4 O-6) was isolated and structure was investigated by X-ray crystallography. It crystallizes in the monoclinic space group P2(1)/c with cell parameters a = 9.704(1) Angstrom, b =12.580(2) Angstrom, c = 13.684(8) Angstrom, Z = 4. The molecules appear to be stacked.