The hearth of the A 17 open air campsite of the Magdalenian settlement of Etiolles (Essonne, France) consists of a small depression surrounded by two rings composed mostly of sandstone blocks, wedged by a few limestone and coarse-grained limestone fragments. The study of its characteristics tends to solve the particular problems which are bound to its nature, its organization and its function. The contribution of thermoluminescence (TL) analyses to such a study enables us to specify and explain the results obtained from archaeological methods only. These methods are reassembling the chips from the stones and the visual analysis of the tracks of red or black coloration that spotted the different faces of the stones. When studying the TL glow curves, stones can been arranged in two groups: those for which the heating temperature was too low to erase the geological TL (T inferior or equal to 250 °C) and those which were heated between 300 and 550°C whose geological TL was partially or completely erased. Comparing the measured temperature of the selected samples to their own situations in and around the hearth emphasized the successive settings of its border. -- AATA