Brainstem acoustic evoked potentials (BAEP) in clinically proven brain death are already described in the literature. In most cases there were no reproducable BAEP or only wave I ipsilateral. In a few cases, shortly after the onset of brain death, wave I and a wave II ipsilateral have been detected. 40 Patients were examined during developing brain death and in brain death. Using an ipsilateral and contralateral montage (mastoid/vertex) four different patterns of BAEP in brain death could be distinguished: Wave I ipsilateral and wave II ipsilateral, reduced in amplitude and delayed in latency and a wave I-contralateral, Wave I ipsilateral and wave I-contralateral, Only wave I ipsilateral, No reproducable BAEP. In clinically not brain dead patients, three different patterns of BAEP are recorded which should be known in order to comment on the validity of the method in the diagnosis of brain death: Only wave I and a flat and late wave, only recordable using several reproductions and with a low rate of artefacts. Only wave I recordable while the patient is still breathing spontaneously (false positive results). Reversible loss of wave I. Ignoring the results, the BAEP may lead to false positive results in the diagnosis of brain death.