OBJECT: The aim of this study was to study the effects of MR imaging on the electrical settings of deep brain stimulation (DBS) systems and their clinical consequences. METHODS: The authors studied the effects of 1.5-T MR imaging on the electrical settings of implanted DBS systems, including 1 or more monopolar or quadripolar leads, extension leads, and single- or dual-channel implantable pulse generators (IPGs). The IPG was switched off during the procedure and the voltage was set to 0. The impedances were checked before and after MR imaging. RESULTS: Five hundred seventy patients were treated with DBS for movement disorders and underwent brain MR imaging after lead implantation and before IPG implantation. None of the patients experienced any adverse events. Thirty-one of these patients underwent 61 additional MR imaging sessions after the entire DBS system had been implanted. The authors report neither local cutaneous nor neurological disorders during or after the MR imaging session. No change in the IPG settings occurred when the magnet reed switch function remained disabled during the procedure. CONCLUSIONS: This study demonstrates that 1.5-T MR imaging can be performed safely with continuous monitoring in patients with a DBS system. The ability to disable the magnet reed switch function of the IPG prevents any change in the electrical settings and thus any side effects. The increasing number of DBS indications and the widespread use of MR imaging indicates the need for defining safety guidelines for the use of MR imaging in patients with implanted neurostimulators.