Background: Central corneal thickness greater than 0.520 mm causes true intraocular pressure to be overestimated when the technique of applanation tonometry is used to measure intraocular pressure. Objective: To compare the corneal thickness measurements of patients enrolled in a study of ocular hypertension with those of age-matched control subjects with normal intraocular pressure. Methods: Central corneal pachymetry using an optical pachymeter was performed on each study subject (n=55) at baseline and in an independent sample of control subjects. A 2 sample, 2-tailed t test was used to compare the 2 populations. Results: The patients with ocular hypertension had significantly higher mean corneal thickness measurements (mean±SD, 0.594±0.037 mm) than the control group (0.563±0.027 mm) (P<.001). Conclusion: Corneal thickness may be a confounding factor in the measurement of intraocular pressure, and this may modify the risk for progression to glaucoma in patients with ocular hypertension.