The overall aim of this thesis was to study the effects of deep brain stimulation (DBS) in patients with refractory obsessive-compulsive disorder (OCD). First, we evaluated the current standard of DBS for patients with treatment-refractory OCD. For this, we investigated effectiveness and adverse effects of DBS in a naturalistic, clinical setting. In addition, we looked at long-term outcomes of DBS in patients with OCD, including on quality of life and functioning. The second goal of this thesis was to improve patient selection by identifying predictors of response to DBS, and by addressing specific co-morbidities that may affect clinical outcome. At last, DBS is a treatment that consists of 3 phases; implantation of the electrodes, modulation of the effect by optimizing electrode settings and consolidation of results on the long term. In the third part of this thesis we conducted studies that focused on how to advance these three phases. We investigated (I) a technique to improve electrode targeting, (II) a new stimulation paradigm (cyclic DBS) aimed to reduce adverse effects, by performing a randomized controlled clinical trial, and (III) the additional effects cognitive behavioral therapy to consolidate clinical outcomes. Ultimately, the goal was to improve the overall results of DBS for OCD and add to the academic discussion about the place of DBS in the treatment of OCD.