Direct electrical transport measurements in a diamond anvil cell provide evidence for the metallization of cesium iodide (Csl) at a pressure of 115 gigapascals, A drop in the temperature dependence of the resistance was found at pressures above 180 gigapascals, indicating that the Csl was superconductive. The superconductivity changed under the influence of a magnetic field to a Lower critical temperature ana disappeared above 0.3 tesla. The highest critical temperature at which superconductivity was observed was 2 kelvin, and the critical temperature decreased with increasing pressure.