The crystal structure of the copper(I) iodide pyridine adduct has been determined by X-ray diffraction at 295 K and refined by least squares to R 0.057 for 2 710 ‘observed’ reflections. Crystals are orthorhombic, space group P212121, with a= 16.032(6), b= 15.510(2), and c= 11.756(3)Å. The asymmetric unit is Cu4I4py4, based on the well-known tetrahedral tetrameric Cu4I4 unit, with Cu–N 2.04, Cu–I 2.70, and Cu–Cu 2.69 Å; the latter distance is much shorter than in the analogous complexes formed with phosphine and arsine ligands.