The purpose of the study was to quantify the variation of central corneal thickness (CCT) in an east Asian population and to examine its relationship to estimates of intraocular pressure (IOP) made with an applanation tonometer. The study design was a cross-sectional, population-based survey. One thousand two-hundred forty-two residents of Hövsgöl Province, Mongolia, 10 to 87 years of age participated. The CCT was measured using an optical pachymeter in all subjects. The IOP was measured using a, Goldmann-type applanation tonometer in subjects 40 years of age and older. There was a highly significant decrease in CCT with age: 5 microns/decade in men and 6 microns/decade in women (both, P < 0.0001). A highly significant positive correlation was identified between IOP and CCT. Linear regression analysis suggests that between the ages of 40 and 80 years, an increase in CCT of 10 microns is associated with an increase in IOP measurements of 0.18 mmHg in right eyes (95% confidence interval, 0.12-0.25) and 0.24 mmHg in left eyes (95% confidence interval, 0.17-0.31). The authors calculate that interindividual differences in CCT may produce a difference in measured IOP of between 2.3 and 3.1 mmHg. Variation in CCT is a significant source of variation in IOP measurements between individuals. The authors suggest that measurement of corneal thickness should be considered when assessing IOP as a risk factor for glaucoma in east Asians.