Dark-green platy crystals of the new compound Pb₃₁O ₂₂Br₁₀Cl₈ (1) have been obtained by rapid quenching of a lead oxide halide melt. The structure of 1 (triclinic, P1, a = 12.1192(7) Å, b = 16.2489(10) Å, c = 18.3007(11) Å, α = 93.104(2)°, β= 95.809-(2)°, γ = 111.252(1)°, V = 3325.4(3) ų, Z = 2) can be viewed as incorporation of [PbX₆]^4- halide units (X = Br, Cl) into the defect PbO matrix. The latter represents a two-dimensional [O₂₂-Pb ₃₀]¹⁶⁺ cationic layer of OPb₄ tetrahedra that can be derived from the [OPb] tetrahedral layer observed in tetragonal PbO. The layer consists of 22 symmetrically inequivalent OPb₄ tetrahedra and represents the topologically most complicated arrangement of tetrahedra known to date.