(Phenacetin)4·2I4·2H2O is triclinic,a= 13.641 (7),b= 12.807 (6),c= 7.201 (3) Å, α = 99.8 (4), b̃ = 86.5 (4), γ = 104.0 (5)°,P1, Z = 1. The ordered crystal structure has been refined toRF= 0.050, using 4173 independent reflections measured on a four‐circle diffractometer with MoKa(graphite monochromator) radiation. The crystals are composed of alternating positively and negatively charged slices; each positive slice contains a double layer of stacks of hemi‐protonated phenacetin molecules which are H‐bonded through their carbonyl groups (d(O ‐ ‐ ‐ O) = 2.432 (4) Å) while each negative slice contains a single layer of I2−4‐ions linked in chains along [100] through H‐bonds to pairs of water molecules. The axes of the phenacetin stacks are parallel to the planes of the (I2−4·2H2O)‐layers. The I2−4‐ion is centro‐symmetric and can be approximately represented as I−‐ ‐ ‐ I–I‐ ‐ ‐ I−(d(I−‐ ‐ ‐ I) = 3.404 (1) Å; d(