CuInS2 thin films have been prepared by reactive magnetron sputtering from metallic targets in an Ar/H2S atmosphere. The Cu/In ratio and substrate temperature have been varied and absorber layers were processed to solar cell devices using the HMI baseline process. Device efficiencies up to 8.8 % have been achieved. The electronic and optical properties of the solar cell devices were analyzed by Scanning Electron Microscopy, Raman, photoluminescence, current-voltage and quantum efficiency measurements. Raman measurements indicate that Cu-Au defect ordering is present in some of the films, which can be eliminated by appropriate choice of the growth parameters. Photoluminescence measurements show spectra very similar to the spectra found for cells from the two-step sequential process indicating a similar defect structure in these films. No principle obstacles to establishing a one-step reactive magnetron sputtering process for CuInS2 solar cell absorbers have been identified.