Osteoid Osteoma represents 10% of all benign bone tumors. It is composed of a highly vascularized nidus of connective tissue and trabeculae of newly formed osseous tissue surrounded by peripherical dense sclerotic bone ( 1 ) . Periosteal bone reaction is variable and the intensity of it depends on the location either cortical or subperiosteal of the lesion . It presents in ages comprehended between 1 and 63 years of age with a mean age of 17 years and in 85 % of the cases it characteristically affects young patients between 10 and 25 years ( 2 ). There is a male to female ratio of 2:1. Clinically the hallmark of this lesion is pain not related to physical activity but on the contrary , being increased by repose , and clearly most prominent at night . It disappears immediately ( 20-30 min ) after the administration of salicylates . It seems that the synthesis of Prostaglandins by the tumor is closely related to the genesis of the pain. Sometimes they may be painless specially those presenting in the hand. Periarticular and intrarticular lesions often present with vague joint pain and synovitis, even deformity or shortness of the extremity. Spinal lesions produce painful scoliosis concave to the side of the tumor.There is no evidence of progression and malignant degeneration of this benign tumor. Transformation into osteoblastomas have been described in some rare cases and also spontaneous healing in a mean period of 5 years ( 3 ).Half of the lesions are located in the femur ( specially the proximal region ) and tibia. 13 % occur in the spine ( 90% involving posterior elements and 10% vertebral body ). Other locations are humerus, hand (8%) and foot (4%). Normally they affect long bone diaphysis although they can occur also in metaphysis or epiphysis (subarticular). The size of the nidus may vary in between 1 and 15 mm .It may be completely osteolytic or totally calcified, but the most common presentation is a unique central calcification surrounded by an osteolytic halus which at the same time is surrounded by reactive bone sclerosis. Periosteal bone reaction is frequently solid and rarely lamilated , obscuring sometimes the nidus.Computed Tomography (CT) is the technique of election to demonstrate the nidus. The central nidus may be hot on Scintigraphy . MR imaging detects soft tissue and marrow edema that sometimes may confuse the diagnosis. Ultrasound can be useful in certain cases.Differential diagnosis includes osteoblastoma, osteomyelitis ( Brodie Abscess ), arthritis, stress fracture and enostosis. Medical treatment with salycilates has proved healing after 3-6 years of treatment, being the initial therapeutic option. Non the less this option has the inconvenient derived from the secondary effects due to this drugs and also the low tolerance of patients to maintain long term treatments. The classic treatment used has been surgical excision of not only the osteoid osteoma but also the normal surrounding bone. Surgery presents difficulty identifying and locating the lesion being frequent the recurrences due to incomplete excisions. In other cases locating the lesion at surgery is so aggressive that surgeons are obliged to perform secondary osteosynthesis techniques. Finally complications such as stress fractures and any other complication due to surgery including long term hospital stay have been described.There are some methods used to locate more precisely the nidus, some of them have already been abandoned such as the use of Tetracycline which accumulates in mineralized bone fluorescending under ultraviolet light, or Radionuclide labelling. Other authors (5) prefer the direct location of the nidus cutting gradually the layers of the reactive bone , and removing the nidus with minimal excision of the normal surrounding bone. During the past 10 years different authors have published their experience with CT guided percutaneous removal of osteoid osteomas. Percutaneous excision using large-caliber hollow needles and drills was first described in 1986 and , although with different modalities, has been and is still widely used .The procedure is performed under epidural or general anaesthesia. Patients remain under hospital observation during a few days and must avoid resting on the affected extremity at least during the first weeks. Destruction of the nidus by means of alcohol inyection , interstitial laser photocoagulation (3), or radiofrequency ablation , although they all require general anaesthesia or active sedation, allow hospital discharge of the patient during the first 24 hours after treatment without any physical restriction.Percutaneous radiofrequency ablation was first used for trigeminal neuralgias treatment . Tillotson and Cols. (9) first described this tecniques results on a dogs femur. Rosenthal and Cols. (10) published in 1992 the first article presenting a series of 4 cases of osteoid osteoma treated with percutaneous radiofrequency ablation . From this work on , few series have been published about this therapeutic alternative (11-14). We present our  experience with percutaneous radiofrequency ablation using a "cool-tip" electrode .