The intermixing of roquesite (CuInS2) and kesterite (Cu2ZnSnS4), i.e. Cu(In-x(ZnSn)(1-x)S-2 was investigated by a combination of neutron and X-ray powder diffraction. Samples with 0 <= x <= 1 were synthesized by a solid state reaction of the pure elements in evacuated silica tubes at 800 degrees C and cooled with a 10 K/h rate after the final annealing. The structural parameters of CuInx(ZnSn)(1-x)S-2 were determined by simultaneous Rietveld refinement of neutron and X-ray diffraction data. The microstructure and chemical composition of the samples were investigated by electron microprobe analysis. A broad miscibility gap exists in the region 0.4 <= x<0.8 indicated by the coexistence of two phases. an In-rich (x similar to 0.77) and a Zn-Sn-rich (x similar to 0.33) phase. Cu(In-x(ZnSn)(1-x)S-2 mixed crystals with 0 <= x<0.4 crystallize in the kesterite type structure, and with 0.8 <= x <= 1.0 in the chalcopyrite type structure. In the latter In, Zn and Sn are disordered on the In site. In the mixed crystals the lattice constant a and c show a linear dependence on chemical composition, whereas the tetragonal deformation Delta = 1-c/2a varies nonlinearly. Moreover in the mixed crystal with x similar to 0.15 the tetragonal deformation is equal zero and thus its structure is characterized by a pseudo-cubic unit cell. (C) 2008 Elsevier B.V. All rights reserved.