The synthesis of the CuInGeS4 compound was performed in a shaft-type furnace by the single-temperature method realized by the gradual heating of the samples (heating rate of 10 K/h) to 1370 K with an intermediate exposure to 820 K for 36 h. The annealing was performed at 670 K for 250 h. The synthesis process was finished after quenching the samples into cold water. The phase diagram of the CuInS2-GeS2 system was investigated using XRD, differential thermal and microstructure analyses. Two different processes take place in the system, a peritectic one, with the peritectic point coordinates 75 mol% GeS2, 1108 K, and a eutectic one at 86 mol% GeS2, 1033 K. The crystal structure of CuInGeS4 was studied by the powder method. The compound crystallizes in the tetragonal symmetry, space group I-4 (structural type CdGa2S4), with the lattice parameters a = 0.55492(2) nm, c = 1.00282(6) nm. Atomic parameters were calculated in the anisotropic approximation, with R-I=0.0680 and R-P=0.1315. (C) 2011 Elsevier B.V. All rights reserved.