The phase diagram of the system CdI2-Ag2Se is studied by means of X-ray diffraction, differential thermal analysis and measurements of the density of the material. The unit cell parameters of the intermediate phase 2CdI(2)center dot 3Ag(2)Se were determined a = 0.6387 angstrom, b = 4.311 angstrom, c = 4.044 angstrom; alpha = 113.72 degrees, beta = 90.27 degrees and gamma = 94.85 degrees. The intermediate phase 2CdI(2)center dot 3Ag(2)Se has a polymorphic transition at 125 degrees C. It melts incongruently at 660 degrees C. (C) 2006 Elsevier B.V All rights reserved.