OBJECTIVE To determine: (i) the outcome of the ice-water test (IWT) in patients with an overactive detrusor and to define the sensitivity of the test in differentiating bladder instability from detrusor hyper-reflexia: and (ii) to investigate any differences in sensitivity to the IWT with detrusor hyper-reflexia caused by suprapontine and spinal pathologies. METHODS Of 130 consecutive patients with urinary symptoms who underwent a urodynamic evaluation and IWT, 80 had detrusor overactivity; of these 60 had detrusor hyper-reflexia and 20 had bladder instability. The patients with detrusor hyper-reflexia were further subdivided into two groups, suprapontine or spinal, based on the site of the neurological lesion. RESULTS The overall sensitivity of the test in patients with detrusor hyper-reflexia was 65% and the specificity 85%. In patients with a spinal pathology causing detrusor hyper-reflexia, the test was positive in 70%, while 46% with suprapontine causes of detrusor hyper-reflexia had a positive test. CONCLUSIONS Although 65% of the patients with detrusor hyper-reflexia and known neurological disease had a positive IWT, so did 15% of the patients with no neurological disease and bladder instability. Patients with suprapontine pathology had a lower sensitivity than those with infrapontine pathology, but this was not statistically significant. The relatively larger number of false-negative tests in patients with a suprapontine pathology is one reason why the test is insufficiently sensitive to discriminate between detrusor hyper-reflexia and bladder instability.