We developed a new method of imaging the anterior segment of the eye using high-frequency ultrasound that allows structural details of the angle, iris, ciliary body, zonule, and posterior chamber to be visualized and measured at microscopic resolution in living patients. We applied the term ultrasound biomicroscopy to this technique, which we used to image anterior segment structures in a series of nine normal subjects. We provide a system of definition for anterior segment measurements that will allow reproducible measurements to be performed in the future. Measurements in normal subjects provide a foundation for future studies of specific glaucoma types and facilitate comparison of normal and glaucomatous eyes. Images in several specific types of glaucoma were obtained to exemplify the potential of this technique.