Following the development of gray-scale imaging, real-time scanning, Doppler examination, and high-frequency sonography, endosonography is one of the latest major breakthroughs in the history of diagnostic ultrasound. Although early attempts at inserting ultrasound transducers in natural cavities of the body can be traced back more than two decades, only in the past few years has technology allowed the development and commercialization of effective, easy-to-use endosono­ scopic probes. Because the transducer can be placed in direct contact with or close to lesions, high frequencies (up to ~2 MHz) can be used, yielding cross-sectional images of unsurpassed resolution. The availability of specially designed intracorporeal probes for specific natural cavities that are routinely explored by conventional (optical) endoscopy or palpation has significantly expanded the diagnostic applications of sonography. Transrectal and transvaginal examinations are now performed routinely in many institutions, and virtually all sonographic equipment manufac­ turers have in their line of products at least one endorectal and one endovaginal transducer. Most endosonoscopic probes connect to existing scanners, and for radiology departments, the invest­ ment for transrectal or transvaginal scanning will usually be limited to the purchase of the specific probe. In this book, clinical applications of endosonography (excluding transesophageal echocardio­ graphy) are covered by European and North American experts. Current equipment and techniques of examination are described in detail to help newcomers get started in the field of endosonography.