The structure of the superconducting copper oxychromate Tl 3 (CrO 4 )Sr 8 Cu 4 O 1 6 has been determined from powder neutron diffraction data. This compound derives from the @'1201@' classical structure by an ordered substitution of CrO 4 groups for thallium oxygen polyhedra showing definitively that chromium is hexavalent. The main features that characterize this original structure deal with the waving character of the [CuO 2 ] ∞ layers, and the absolute planar character of the [(TlCr),O] ∞ layers. In the [(TlCr),O] ∞ layers, the thallium and oxygen atoms form triple ribbons of edge-sharing TlO 4 tetrahedra and TlO 6 octahedra running along a, whereas the CrO 4 tetrahedra are displayed in rows running along a, but are disconnected from each other and from the other polyhedra in the layer. Two kinds of CuO 6 octahedra are observed, whose distortions originate from their connection with different polyhedra along c. The great flexibility of the two kinds of layers, and the structural analogy with copper oxycarbonates are emphasized.