Although there are effective treatments available for many, probably most, patients with OCD, a significant number do not respond, or fail to experience a sustained beneficial response. For patients with such chronic, disabling and 'treatment-refractory' OCD, neurosurgical treatments may be considered. The best-established neurosurgical treatments are so-called ablative procedures, where targeted lesions are created with the intention of interrupting and modifying specific circuitry functions. There is a lengthy history of such procedures and a substantial literature although this is largely of an observational nature. However, both stereotactic radiosurgery (gamma knife) and MR-guided high intensity focused ultrasound are methods of lesion generation that lend themselves to the conduct of blinded randomised trial designs and these are beginning to be utilised. In this Chapter, we present a narrative review of the key recent literature that describes the evidence for the safety and efficacy of lesion procedures for OCD. For context, we also consider the strength and quality of evidence relating to intensive residential treatment for OCD (sometimes proposed as an alternative to neurosurgery), furthermore, we also present some comparative data for lesion surgery and deep brain stimulation (DBS).