A method and a device for determine a core body temperature from a flow of heat from the body to a neutral medium via a first sensor element and a second sensor element. A dynamic model is used that describes heat flow with a plurality of parameters including the core body temperature, a first sensor element temperature, and a second sensor element temperature. The first sensor element is arranged on a surface of the body. One of the parameters and the core temperature are estimated such that a difference is minimized between the temperatures indicated by the sensor elements, and the temperatures resulting from the dynamic model at the first and second sensor elements for a plurality of time points which lie temporally prior to a specific time point. An estimated core temperature, where this difference has been minimized, is the core body temperature to be determined.
