An unusual case is presented of a patient with an acoustic neuroma, in whom the responses recorded with the usual derivation of ipsilateral recording and stimulation resulted in a normal response, whereas that derived contralaterally was abnormal. The patient was also reported to have a normal magnetic resonance scan although the tomograms revealed a widening of the internal auditory meatus and subsequent histology confirmed a schwannoma. Postoperatively the hearing was preserved and the brainstem responses showed a typical ‘acoustic picture’ with a delay of Waves III and V both ipsi and contralaterally. Subsequent testing showed an improvement in the latency of Wave V. Certain hypotheses are advanced regarding the mechanism involved in the latency differences observed between ipsi- and contralateral recordings, but the significance of abnormal prolongation of the latencies of certain components occurring independently in the contralateral response remains obscure. However, this patient's example clearly shows its value in clinical testing.