Background: To report the preliminary outcomes from the prospective, nonrandomized, multicenter study of the OsteoCool Radiofrequency Ablation system used for the palliative treatment of patients with painful bone metastases (OPuS One Study). Methods: Subjects were prospectively enrolled (NCT03249584) from October 2017 through August 2018. Inclusion criteria were: 2 or less painful target sites involving the thoracolumbar spine, pelvis and/or sacrum, with a worst pain ≥4/10 measured by the Brief Pain Inventory (BPI) within the previous 24 hours. RFA was performed with the OsteoCool device (Medtronic) under imaging guidance and followed by cementoplasty at operator discretion. Subjects were evaluated prior to RFA, at discharge, 3 days, 1 week, and 1-, 3-, 6-, and 12-months. Demographics and disease characteristics were collected at baseline and outcomes were assessed using validated measures. Device-, procedure- and/or therapy-related adverse events (AEs) were collected. Results: At the time of the analysis, 37 subjects at 8 US centers underwent RFA. The mean age was 64 years (range 30-89) and 68% were female. Mean baseline BPI worst pain was 8.6. The most common histology was adenocarcinoma; breast (32%) and lung (24%) were reported as the most common primary cancer. Thirty-one subjects (84%) were treated for lesions involving the thoracolumbar spine, while 6 subjects (16%) were treated for lesions located the pelvis and/or sacrum. All RFA procedures were technically successful. Of the 14 subjects presenting at the 3-month visit, 93% did not undergo radiation therapy at the targeted site(s) between baseline and 3 months. Seventy-four percent (25/34) of subjects at 1 week and 93% (13/14) of subjects at 3 months reported a clinically significant change from baseline in worst pain of ≥ 2 points. One AE, drug hypersensitivity, resolved without intervention. All eleven deaths reported were attributed to the subjects underlying malignancy and not related to RFA. Conclusions: The preliminary results of the OPuS One study show rapid pain improvement at 1 week and sustained long-term relief through 3 months in patients with metastatic bone disease. Clinical trial information: NCT03249584