Focused ultrasound technology provides a noninvasive modality for tissue ablation. Although widely used for the treatment of benign prostatic hyperplasia, its application for the treatment of localized prostate cancer is controversial, and its use for the treatment of small renal masses remains experimental. This article outlines the underlying principles of thermal focused ultrasound technology and its limitations as evident in the current literature. The principles and technique of nonthermal cavitational ultrasound tissue ablation is described with a summary of preliminary experimental data.