Objective: Central corneal thickness influences intraocular pressure (IOP) measurement. We examined the central corneal thickness of subjects in the Ocular Hypertension Treatment Study (OHTS) and determined if central corneal thickness is related to race. Design: Cross-sectional study. Participants: One thousand three hundred one OHTS subjects with central corneal thickness measurements. Intervention: Central corneal thickness was determined with ultrasonic pachymeters of the same make and model at all clinical sites of the OHTS. Main Outcome Measures: Correlation of mean central corneal thickness with race, baseline IOP, refraction, age, gender, systemic hypertension, and diabetes. Results: Mean central corneal thickness was 573.0 ± 39.0 μm. Twenty-four percent of the OHTS subjects had central corneal thickness > 600 μm. Mean central corneal thickness for African American subjects (555.7 ± 40.0 μm; n = 318) was 23 μm thinner than for white subjects (579.0 ± 37.0 μm; P < 0.0001). Other factors associated with greater mean central corneal thickness were younger age, female gender, and diabetes. Conclusions: OHTS subjects have thicker corneas than the general population. African American subjects have thinner corneas than white subjects in the study. The effect of central corneal thickness may influence the accuracy of applanation tonometry in the diagnosis, screening, and management of patients with glaucoma and ocular hypertension.