Thallium activated cesium iodide is discussed as a gamma-ray spectrometer which should have advantages over thallium activated sodium iodide at high gamma-ray energies. Data are presented which were obtained with a five-inch diameter by three and one half-inch high right cylinder of thallium activated cesium iodide viewed with a three-inch diameter photomultiplier. These data include linearity of response from 80 kev to 7.2 mev, resolution as a function of gamma-ray energy, and photofractions as a function of gamma-ray energy for collimated radiation.