To examine the relation of refractive errors to glaucoma and intraocular pressure (IOP) in a defined white population. Population-based cross-sectional and follow-up study. Persons aged 43 to 86 years living in Beaver Dam, Wisconsin (n = 4926). All participants received a standardized assessment of refraction, IOP, and glaucoma at baseline (1988-1990), with IOP remeasured 5 years later (1993-1995). Refraction was defined at baseline as follows: myopia as spherical equivalent of -1.00 diopters (D) or less, emmetropia as -0.75 to +0.75 D, and hyperopia as +1.00 D or more. Relation of baseline refraction to prevalent glaucoma (defined from IOP, optic disc, and visual field criteria) and incident ocular hypertension (defined as IOP more than 21 mmHg at the 5-year examination in eyes with IOP of 21 mmHg or less at baseline). A myopic refraction was correlated with increasing IOP at baseline (P < 0.001). After controlling for age and gender, persons with myopia were 60% more likely to have prevalent glaucoma than those with emmetropia (odds ratio [OR], 1.6; 95% confidence interval [CI], 1.1, 2.3). In contrast, controlling for age, gender, and baseline IOP, persons with hyperopia were 40% more likely to have incident ocular hypertension than those who were emmetropic at baseline (OR, 1.4; 95% CI, 1.0, 2.0). Myopia was not related to incident ocular hypertension. In these population-based data, there was a cross-sectional association of myopia with higher IOP and prevalent glaucoma. Similar associations have been found in previous studies. Hyperopia may be associated with 5-year risk of ocular hypertension, a finding that needs further investigation.