Preoperative evaluation and surgical planning for penetrating keratoplasty in patients with dense corneal scars is often difficult because of poor visualization of the anterior segment. We performed ultrasound biomicroscopy (50-megahertz frequency, 50-micron resolution) on five eyes of five patients with dense corneal opacities of different etiologies to evaluate the anatomic relationships of the iris, lens, angle, and ciliary body. Corneal thickness, the presence or absence of iridocorneal adhesions, peripheral anterior synechiae, and cyclitic membranes, intraocular lens position, and relationships among intraocular structures could be evaluated in vivo. Ultrasound biomicroscopy is the optimal method of obtaining reliable, high-resolution images delineating anatomic relationships and pathology in the anterior segment. This information aids in surgical planning for penetrating keratoplasty and anterior segment reconstruction.