The objective of this study was to evaluate the effects of a moderate, intraischemic hypothermia on the behavorial deficits up to 4 weeks after induction of a focal mass lesion. A focal epidural mass lesion was induced by an epidural balloon. The severity of the trauma was defined by the balloon volume and flattening of electroencephalography. Hypothermia (32 degrees C) was induced as soon as maximum balloon infIation was reached. Ischemia was extended over 30 min. After reperfusion, normothermic (n = 24) and hypothermic animals (n = 25) were monitored for 3 h followed by a rewarming of the cooled animals. Results were compared to sham-operated animals (n = 10). Behavioral deficits were assessed by postural reflex (PR), open field (OF), beam balance (BB), beam walking (BW), and water maze tests (WMT). MRI follow-up and histology was evaluated. Sham-operated rats showed normal test results. Rats with normothermia showed worsening of test performance (PR, p < 0.05; OF, p < 0.05; BB, p < 0.05; BW, p < 0.05; WMT, p < 0.05) compared to controls over the whole observation period. A significantly better behavioral outcome was observed in animals treated with hypothermia which showed no differences from controls 3-4 days after injury (PR, OF, BB, BW, WMT, p > 0.05). Lesion induced mortality was reduced in cooled animals but overall mortality rates were not influenced by this therapeutic measure. Neuronal cell loss in the CA1-CA4 region (p < 0.05) was reduced and the lesion size smaller (21%/p > 0.05) in hypothermic animals. Magnetic resonance imaging revealed that the lesion was more pronounced in the cortical grey matter after normothermia, whereas hypothermic animals showed more subcortical brain lacerations. In conclusion, intraischemic hypothermia significantly improved the behavioral outcome, and decreased lesion-induced mortality and the size of the lesion after an epidural focal mass lesion.