BACKGROUND: It is believed that the brain temperature is about 1oC higher than the peripheral temperature. However the result has been mostly obtained in normothermia patients. The objective of this study was to evaluate whether the brain and axillary temperature difference would be increased or decreased in hypothermic patients. METHODS: Sixty-six patients who underwent a craniotomy with implantation of the thermal diffusion flowmetry sensor (SABER 2000; Flowtornics, Phonics, USA) were included in this study. The temperature of the cerebral cortex and axilla were measured simultaneously every 2 hours. The patient groups were divided according to their axillary temperature, hyperthermia (over 38oC: 127 paired data), normothermia (36 38oC: 1626 paired data) and hypothermia (under 36oC: 285 paired data). A total 2048 paired sample data were collected and analyzed. RESULTS: The temperature difference between the cerebral cortex and the axilla was 0.46 +/- 1.04 oC in hyperthermic patients, 0.89 +/- 1.65 C in normothermia patients and 1.04 +/- 0.82 C in hypothermic patients. The temperature difference has statistical significance in each group (unpaired t-test, P > 0.05). CONCLSIONS: Our results demonstrate that the temperature difference in the brain shows a difference according to the patients, body temperature. In normothermia the temperature difference between the brain and the axilla was about 1oC. However in a hyperthermic state, the temperature difference decreased and in a hypothermic state, the temperature difference increased.