All participants will receive ALIC DBS for OCD. DBS received a Humanitarian Device Exemption (HDE) in 2009 with an indication for bilateral stimulation of the ALIC as an adjunctive treatment to medications and as an alternative to anterior capsulotomy for treatment of chronic, severe, treatment-refractory OCD in adult patients who have failed at least three SSRIs. Additionally, more stringent criteria have been selected for defining treatment-resistance in this protocol, as indicated below.  INCLUSION CRITERIA:  18 years of age or older Primary psychiatric diagnosis of Obsessive-Compulsive Disorder (OCD, per DSM-5 criteria) Meets FDA Humanitarian Device Exemption (HDE) criteria for indication Has elected to receive clinically indicated DBS for OCD with a directional system outside of this research study, as determined by treating clinician(s) and per current clinical practice Minimum of a five-year history of treatment-refractory OCD with substantial functional impairment Failure of an adequate trial of at least three of the following SSRIs: Fluoxetine, Fluvoxamine, Citalopram, Escitalopram, Sertraline, Paroxetine Failure of an adequate trial of clomipramine Failure of an adequate trial of one or more of the aforementioned antidepressants in combination with at least one of the following augmentation agents: Haloperidol, Risperidone, Olanzapine, Quetiapine, Ziprasidone, Aripiprazole Failure of an adequate trial of Cognitive Behavioral Therapy (CBT), defined as 25 hours of documented exposure and response prevention (ERP) by an expert therapist Minimum score of 25 on the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) at preoperative baseline Ability to undergo preoperative MRI English proficiency Capacity to provide written informed consent Willing and able to comply with all device operation and study-related procedures  EXCLUSION CRITERIA:  Ineligible or unwilling to receive ALIC DBS for OCD Contraindications for general anesthesia, neurosurgery, or an MRI scan Neurological disorder or other significant brain pathology, such as moderate / marked cerebral atrophy, stroke, tumor, epilepsy, or previous neurosurgical procedures (excluding cingulotomy, which may be permitted if not contraindicated in the opinion of implanting neurosurgeon) Unstable medical illness, chronic immunosuppression, and/or considerably reduced life-expectancy Conditions requiring anticoagulant therapy which cannot be discontinued for the perioperative period, as required Conditions requiring certain regular MRI scans or diathermy Currently implanted with a cardiac pacemaker / defibrillator or other implanted electrical device which may interfere with DBS stimulator or the function of which may be impacted by its implantation, in the opinion of evaluating neurosurgeon Other primary Axis I disorder or history of psychosis, such as schizophrenia, psychosis in the context of depressive or manic episode. Current or past history within the 6 months prior to DBS implantation of substance abuse or dependence (excluding nicotine and caffeine) Active suicidal ideation with intent, suicide attempt within the last six months, more than three suicide attempts within the last two years, or serious suicide risk as determined by the study psychiatrists Axis II disorders which, in the opinion of the study psychiatrist, may increases the risk of DBS to participants or cause study non-compliance Patients who lack the capacity to for proper device usage and maintenance, in the opinion of the research team Women who are pregnant