The synthesis and characterization of 1,5-diamino-1,2,3,4-tetrazolium perchlorate were carried out. Experimental evidence strongly supports the protonation of a nitrogen atom of the tetrazole ring, including the structure observed in a single crystal X-ray diffraction study of the title compound. Quantum chemical calculations were performed at the CCSD(T)/6-311G(2df,p)// MP2/6-311G(d,p) level of theory to determine the relative energies of all possible N-protonated structures of the 1,5diamino-1,2,3,4-tetrazole ring. The predicted geometry of the most stable isomer compares favorably with the experimentally observed structure.