In the crystal of the title co-crystalline adduct, C8H16N4·C8H9ClO, (I), prepared by solid-state reaction, the mol-ecules are linked by inter-molecular O-H⋯N hydrogen bonds, forming a D motif. The aza-adamantane structure in (I) is slightly distorted, with N-CH2-CH2-N torsion angles of 10.4 (3) and -9.0 (3)°. These values differ slightly from the corresponding torsion angles in the free aminal cage (0.0°) and in related co-crystalline adducts, which are not far from a planar geometry and consistent with a D 2d mol-ecular symmetry in the tetra-aza-tri-cyclo structure. The structures also differ in that there is a slight elongation of the N-C bond lengths about the N atom that accepts the hydrogen bond in (I) compared with the other N-C bond lengths. In the crystal, the two mol-ecules are not only linked by a classical O-H⋯N hydrogen bond but are further connected by weak C-H⋯π inter-actions, forming a two-dimensional supra-molecular network parallel to the bc plane.