The corneal diameter was recorded and the ocular axial length measured by A-scan ultrasonography in 31 eyes of 17 children (ages 0.05 to 7.0 years) who had undergone or were about to undergo surgery for primary congenital glaucoma. These measurements were also done in 60 normal eyes of 33 children (ages 0.20 to 9.6 years) undergoing nonophthalmic surgery. Both measures were usually greater than normal in the glaucomatous eyes. However, the corneal diameter was more sensitive than the axial length in identifying congenital glaucoma. The axial length measurement did not provide additional useful information for any of the eyes. We conclude that the corneal diameter is a more reliable guide than the axial length in the assessment of congenital glaucoma. A transparent plastic gauge for rapid and accurate measurement of the corneal diameter is described.