In the title molecular complex, [Cu4Cl6O(2-EtTz)(4)], where 2-EtTz is 2-ethyltetrazole (C3H6N4), the central O atom is located on the (4) over bar symmetry site and is tetrahedrally coordinated to four Cu atoms, with Cu - O distances of 1.8966 (4) Angstrom. A very slight distortion of Cu4O from a regular tetrahedron is observed [ two Cu - O - Cu angles are 108.76 (3)degrees and four others are 109.828 (13)degrees]. Each Cu atom is connected to three others via the Cl atoms, forming a slightly distorted Cl octahedron around the O atom, with O ... Cl distances of 2.9265 (7) Angstrom for Cl atoms lying on the twofold axis and 2.9441 (13) Angstrom for those in general positions. The Cu atom has a distorted trigonal-bipyramidal environment, with three Cl atoms in the equatorial plane, and with the N atom of the 2-ethyltetrazole ligand and the mu(4)-O atom in axial positions. The Cu atom is displaced out of the equatorial plane by ca 0.91 Angstrom towards the coordinated N atom of the 2-ethyltetrazole ligand.