Bilateral electrical stimulation of the subthalamic nucleus is being used with increasing frequency as a treatment for severe Parkinson disease (PD). Implantable cardiac defibrillators improve survival in certain high-risk patients with coronary artery disease and ventricular arrhythmias. Because of concern about possible interaction between these devices, deep brain stimulation (DBS) systems are routinely disconnected before defibrillators are implanted in patients with PD and arrhythmia. The authors report on a patient with bilateral subthalamic stimulators who underwent successful placement of an implantable defibrillator. Testing of the devices over a wide range of settings revealed no interaction. The patient subsequently underwent multiple episodes of cardioversion when the ventricular lead became dislodged. There was no evidence of adverse neurological effects, and interrogation of the DBS devices after cardioversion revealed no changes in stimulus parameters. The outcome in this case indicates that DBS systems may be safely retained in selected patients who require implantable cardiac defibrillators.