1,8-Bis(dimethylaminomethyl)naphthalene (DMAMN) is a “proton sponge”, and protonation leads to the formation of a strong intramolecular [NH⋯N] + hydrogen bond. In the recently reported room-temperature structure of the salt [DMAMNH] +·NO − 3, P. Brzezinski, T. Głowiak, E. Grech, Z. Malarski and L. Sobczyk, J. Chem. Soc., Perkin Trans. 2, (1991) 1643, the intramolecular hydrogen bond displays an unusual geometry with a nearly symmetrical position of the H atom implying long NH distances. In order to obtain accurate information on the geometry of this [NH⋯N] + hydrogen bond and to investigate the possible occurrence of disorder, the structure was redetermined at liquid nitrogen temperature (100 K). The salt crystallizes in space group P2 1/c (as at room temperature) with a = 11.004(6), b = 11.5132(6), c = 12.2636(7) Å, β = 91.863(4)° and Z = 4. The structure was refined to R = 0.037 for 2811 unique reflections. Difference Fourier syntheses of the N⋯N region and the results of refinement revealed disordering of the H atoms over two positions. Refinement of the population parameter resulted in stable N(1)H and N(2)H distances of 0.83(6) and 1.04(3) Å, and population parameters of 0.34 and 0.66, respectively. The extremely long NH distance at room temperature may be interpreted as the result of increased disordering at elevated temperatures. Because of the absence of intermolecular NH⋯O hydrogen bonds, the packing is chiefly determined by CH⋯O interactions, all of which involve the charged oxygen acceptors of the nitrate anion. The average C⋯O and H⋯O distances and CH⋯O angles of nine interactions are 3.393, 2.35 Å and 157°, respectively.