PbTe5O11 crystallises with monoclinic symmetry (space group C2/c) and unit cell parameters: a = 18.959(4) Angstrom, b = 4.414(1) Angstrom, c = 25.798(6) Angstrom, beta = 98.12 (1), Z = 8). Its crystal structure has been refined by a full matrix least-squares process to R-1 = 0.037 and wR(2) = 0.068 values, on the basis of 3121 independent single crystal X-ray reflections. It can be described as a Te5O11 three-dimensional network of TeO4 disphensids (distorted TeO4E trigonal bipyramids) sharing corners and edges which contains three kinds of tunnels parallel to the Oy direction. The stereochemically active lone pairs E of tellurium atoms are directed towards the centre of two of them. Lead atoms are inserted in pairs in the third one.