Primary generalized dystonia, also called idiopathic torsion dystonia or dystonia musculorum deformans is a disabling neurological condition which usually starts in childhood, mostly in a lower limb and spreads to other body parts as the disease progresses. Medical treatment is usually ineffective and most patients become wheelchair bound or even bedridden. Recently several case series and one RCT reported favourable results of bilateral deep brain stimulation (DBS) of the globus pallidus internus (GPi) for primary generalized dystonias. However, the number of patients treated with bilateral GPi stimulation is still limited. Therefore, we propose a RCT to investigate whether bilateral DBS of the GPi is an effective and safe treatment in patients with primary generalized dystonia.