We determined the reliability of high-resolution contact B-scan echography for estimating the optic cup size in 56 eyes of 28 patients with glaucoma or ocular hypertension. Two trained observers independently evaluated horizontal and vertical cup/disk ratios in stereophotographs, and two skilled echographers independently estimated optic cup size in photoechograms in a masked fashion. The reliability of echographic interpretation varied (kappa 0.29 to 0.71), but it always exceeded that expected by chance alone, even for cups of 0.3 disk diameter or less. Subtly saucer-shaped cups (three of 50 eyes) and deep cups with intact neuroretinal rims (two of 50 eyes) were misinterpreted echographically. High-resolution contact B-scan echography may provide a useful and reliable estimate of the optic cup size in eyes with opaque media.