A temperature measurement system for a gas turbine engine, the gas turbine engine including, in axial flow sequence, a compressor section, a combustor section having plural fuel spray nozzles, and a turbine section. The temperature measurement system includes one or more optical thermometers, each optical thermometer configured to measure the temperature of a component washed by the working gas of the engine, the or each component being in the combustor section or the turbine section at a first position along the axis of the engine.