Hexamethylenediamine dihydroiodide is monoclinic, with cell dimensions $a=4.85{AA}$, $b=12.77{AA}$, $c=9.73{AA}$, ${eta}=91.5^{circ}$ The space group is $P2_1/c$, with two molecules per unit cell. It has a center of symetry in the molecule. All atomic positions are determined by means of a two-dimensional patterson synthesis and fourier synthesis. The C-N bond distance is $1.48{AA}$ and the C-C bond distances are lying between $1.55{AA}$, and $1.59{AA}$. The iodine atom is bonded by hydrogen bridges of $3.59{AA}{pm}0.1{AA}$ to nitrogen atoms and surrounded by three nitrogen atoms. The hexamethylenediamine chain is zigzag in the hexamethylenediamine dihydrochloride molecules though, it is not zigzag in the hexamethylenediamine dihydroiodide.