We conducted a prospective study of 50 consecutive eyes to determine the accuracy of ultrasonographic mapping of vitreoretinal abnormalities. The 50 eyes, all of which had opaque media, underwent A- and B-scan ultrasonography before undergoing vitrectomy. The location and differentiation of any abnormalities were mapped on a fundus drawing sheet. At the time of vitrectomy, the surgeon independently examined the fundus and recorded his findings on a second drawing sheet. When we compared the two sets of drawings, we found that ultrasonography correctly predicted the position of the retina in 45 of 50 eyes and the presence or absence of macular detachment in 48 of 50 eyes. These two findings are particularly important to the surgeon. Ultrasonography also correctly predicted the presence or absence of posterior vitreous detachment in all 50 eyes, correctly described the exact extents of the retinal detachments in 44 of 50 eyes, and located points of vitreoretinal adhesion in 39 of 50 eyes.