the disclosure is directed to a chronic implantable neurostimulator that supports trial and chronic modes of operation . the implantable neurostimulator can alternatively include one or more sensors that may or may not function differently in trial and chronic modes . in particular , the device is designed to be used as both a trial neurostimulator and a permanent , or chronic , neurostimulator . a trial neurostimulation period is generally desired to evaluate the efficacy of the therapy . a percutaneous or implantable trial neurostimulator is used for the trial neurostimulation period . in most cases , the trial period is successful , in which case the trial stimulator is explanted and replaced with a permanent , i . e ., “ chronic ,” implantable stimulator . in accordance with the disclosure , an implantable neurostimulator supports both trial neurostimulation and chronic neurostimulation in the event trial stimulation is successful . in this manner , the additional surgery ordinarily required for replacement of the trial stimulator can be avoided . instead , the implanted neurostimulation device remains implanted and is reconfigured to transition from trial stimulation to chronic stimulation .