The Cyberknife is an integrated image-guided, frameless radiosurgery system. The physical component includes a compact 6 MV X-band linear accelerator mounted to the mobile arm of a robotic manipulator and a real- time imaging system connected to a remote image registration console. Two orthogonally positioned diagnostic x-ray cameras provide real time images of the patient's internal anatomy during treatment. The images are processed automatically to identify radiographic features, such as skull bone landmarks or implanted fiducials and are then automatically compared with digitally reconstructed image of the patient's planning CT. In this processing, the direction of the radiation beam is continuously re-adjusted to reflect any changes in the patient position. An analysis of the accuracy of the Cyberknife radiosurgery system found that the machine has a clinically relevant accuracy of 1.0 +/- 0.3mm. While clinical results with intracranial lesions are comparable to frame-based radiosurgical technique using gamma-knife or linac, recent experiences demonstrate the potential to broadly expand the scope of radiosurgery to many extracranial sites especially for cancer patients. The major potential benefit of radiosurgical ablation of malignant tumors are relatively short treatment time in an out-patients setting combined with better local control of the tumor with minimal risk of side effects. Cyberknife radiosurgery offers a new and alternative therapeutic modality for the medically inoperable early cancers, previous irradiated sites, and difficult lesions not amenable to open surgery, as a boost therapy with surgery or external radiation therapy or for rapid symptom relief of palliative care patients. While we are encouraged by excellent local control of early clinical experiences of Cyberknife, we also stressed the importance of long term follow-up results.