For this human research, 17 treatment-refractory OCD patients who already received DBS implants for treatment refractory OCD between June 1998 and October 2007 will be included. New patients that complete the protocol on "refining the target for DBS in OCD" will be included in this follow-up study as well. They will be psychiatrically evaluated on regular bases: at least twice yearly in the years two to five after surgery, at least once a year for the years thereafter. The duration of this protocol is indefinite, but spans at least 10 years. The main aim of this study is to investigate the long-term effect of DBS in OCD patients.