Non-stoichiometric phases in the series Co(1 - x)Ni(x)Cr2S4 (0=x<1) were prepared at high temperatures. In the composition range 0=x=0.35 single-phase materials, isostructural with the end-member spinel CoCr2S4 are observed, whereas materials in the composition range 0.85=x<1 adopt the Cr3S4 structure of the end-member NiCr2S4. Rietveld refinements using powder neutron diffraction data demonstrate that in the spinel structure nickel cations are accommodated exclusively at tetrahedral sites and in the Cr3S4 phases at octahedral sites in an ordered defect layer. All single-phase materials are semiconductors. Spinel-type phases appear to be ferrimagnetic with saturation moments in the range 2.4-2.6 µ(B), and Curie temperatures which increase with increasing nickel content. The Cr3S4-type materials exhibit a magnetic behaviour similar to NiCr2S4 and Cr3S4, which are complex antiferromagnets.