This is the protocol for a review and there is no abstract. The objectives are as follows: (1) Primary objectives: 1.1 To determine the efficacy and adverse outcomes of neurosurgical interventions for:(a) Obsessive-compulsive disorder (OCD)(b) Major Depressive Disorder(c) Other Anxiety disorders (Generalised Anxiety Disorder, Panic Disorder and/ or Agoraphobia, Social Phobia/ Social Anxiety Disorder) Each condition will be considered separately. Treatment comparisons will consist of each neurosurgical intervention versus control. The control group is expected to be either waiting list or treatment as usual for ablative neurosurgery, and 'no stimulation' for VNS and DBS. (2) Secondary objectives: 2.1 To establish the relative efficacy of different neurosurgical procedures, attempting to compare directly where possible. Comparisons will not be performed if the data are not sufficient to permit this.2.2 To determine whether different neurosurgical procedures confer differential risks of side effects and adverse outcomes.