The title molecular salt, C5H10N3+·Cl−, was obtained as by-product in the attempted synthesis of a histamine derivative. The terminal amino group of the starting material is protonated. The Cimidazole—C—C—N(H3)+ group in the cation is in an anti conformation with a torsion angle of 176.22 (10)°. In the crystal, cations and anions are linked via N—H...N and N—H—Cl hydrogen bonds, forming a two-dimensional network parallel to (10-1). A single weak C—H...Cl hydrogen bond completes a three-dimensional network.