PURPOSE. To characterize posterior scierai thickness in the normal monkey eye and to assess the effects of acute (15- to 80-minute) and short-term chronic (3- to 7-week) intraocular pressure (IOP) elevations. METHODS. Both eyes of four normal monkeys (both eyes normal) and four monkeys with early glaucoma (one eye normal and one eye with induced chronic elevation of IOP) were cannulated. In each monkey, IOP was set to 10 mm Hg in the normal eye and 30 or 45 mm Hg in the contralateral eye (normal or early glaucoma) for 15 to 80 minutes. All eight monkeys were perfusion fixed, yielding eight low IOP-normal eyes, four high IOP-normal eyes, and four high IOP-early glaucoma eyes. Posterior scleral thickness was measured histomorphometrically at 15 measurement points within each eye, and the data were grouped by region: foveal, midposterior, posterior-equatorial, and equatorial. RESULTS. Overall, posterior scierai thickness was significantly different in the various regions and among the treatment groups (p < 0.0001). In the low IOP-normal eyes, the posterior sciera was thickest in the foveal region (307 μm) and thinner in the midposterior (199 μm), posterior-equatorial (133 μm), and equatorial (179 μm) regions. In the high IOP-normal and high IOP-early glaucoma eyes, the posterior sciera was thinner both overall and within specific regions, compared with the low IOP-normal eyes. CONCLUSIONS. The posterior sciera in the perfusion-fixed normal monkey eye thins progressively from the fovea to the equator and is thinnest just posterior to the equator. Acute and short-term chronic IOP elevations cause regional thinning within the posterior sclera of some monkey eyes, which significantly increases stresses in the scierai wall. Copyright © Association for Research in Vision and Ophthalmology.