OBJECTIVE The aim of this study was to resolve the paradox as to whether magnetic stimulation of sacral nerve roots results in contraction or suppression of the bladder, in both normal individuals and patients with spinal cord injury (SCI). METHODS Seven males with complete SCI and neurogenic detrusor overactivity (NDO) and five normal males were investigated. Bladder capacity and maximum cystometric capacity were determined, respectively, in these groups. Magnetic stimulation was applied to sacral nerve roots using a multi-pulse magnetic stimulator and coil. Stimulation was applied at half capacity, near-full capacity, and during NDO or voiding (in normal individuals). Single and intermittent bursts of stimulation were applied. RESULTS Neither single nor intermittent bursts of magnetic stimulation of the sacral nerve roots resulted in significant bladder pressure rises. Occasionally, following cessation of the magnetic stimulation bladder contractions were seen in patients with NDO. These contractions had an unpredictable and variable latency. As previously reported, magnetic stimulation suppressed NDO in patients with SCI, and suppressed voiding in normal individuals. CONCLUSIONS Bladder contractions are occasionally observed in patients with NDO following withdrawal of stimulation. This phenomenon hypothetically arises as a result of removal of the bladder suppression provided by magnetic stimulation, rather than direct motor pathway stimulation (as has been reported by others). The ability of sacral magnetic stimulation to suppress detrusor contractions is reaffirmed.