The purpose of this study is to examine the long-term effect of Deep Brain Stimulation (DBS) for patients with Parkinson's Disease. We have data for patients operated with DBS since 1998. We wish to examine the effect of stimulation on motor symptoms as well as make a follow-up on complications and side-effects related to treatment. We also wish to follow-up on the quality of life-studies made in the years 2003-2008.