A variety of studies are reviewed in which intraocular pressure (IOP) was determined in defined, general populations. The studies exhibit a remarkably consistent pattern for the frequency distribution of IOP. The distribution conforms well to a normal curve for pressures up to 21 mm Hg, after which a distinct skewness to the right begins to appear. When the data are grouped by age and sex, the degree of right skewness intensifies with age. Mean IOP increases with age. Some studies also show higher mean levels for women than men, but not all do. The arbitrary nature of specifying upper limits of normality is stressed. In addition, the literature is reviewed concerning the arguments for a mixture of two overlapping normal (or lognormal) curves vs a continuum for the distribution of IOP.