The title salt, C(18)H(22)N(5)(+).Cl(-), is a member of a new series of lipophilic 4,6-diamino spiro-s-triazines which are potent inhibitors of dihydrofolate reductase. The protonated triazine ring deviates from planarity, whereas the cyclohexane ring adopts a chair conformation. A rather unusual hydrogen-bonding scheme exists in the crystal. There is a centrosymmetric arrangement involving two amino groups and two triazine ring N atoms, with graph-set R(2)(2)(8) and an N.N distance of 3.098 (3) A, flanked by two additional R(3)(2)(8) systems, involving two amino groups, a triazine ring N atom and a Cl(-) anion, with N.Cl distances in the range 3.179 (2)-3.278 (2) A. Furthermore, the Cl(-) anion, the protonated triazine ring N atom and an amino group form a hydrogen-bonding system with graph-set R(2)(1)(6).