PURPOSE: To quantify the variation in primary open-angle glaucoma (OAG) prevalence with age, gender, race, year of publication, and survey methodology. METHODS: Medline, EMBASE, and PubMed were searched for studies of OAG prevalence. Studies with defined population samplings were sought. Forty-six published observational studies of OAG prevalence (103,567 participants with 2509 cases of OAG) were identified for inclusion in the systematic review and meta-analysis. Data on the number of people and the number of cases of OAG by age, race, and gender were sought for each study. Additional information was obtained regarding whether the definition of glaucoma relied on raised intraocular pressure (IOP) and whether visual field examination was performed routinely on all individuals. Bayesian meta-analysis was used to model the associations between the log odds of OAG and age, race, gender, year of publication, method of visual field testing, and effect of reliance on IOP in the definition of OAG. RESULTS: Black populations had the highest OAG prevalence at all ages, but the proportional increase in prevalence of OAG with age was highest in white populations. The odds ratio per decade increase in age was 2.05 in white populations (95% credible interval, 1.91 to 2.18), 1.61 (95% credible interval, 1.53 to 1.70) in black populations, and 1.57 (95% credible interval, 1.46 to 1.68) in Asian populations. The average estimated prevalence in those older than 70 years of age was 6% in white populations, 16% in black populations, and 3% in Asian populations. After adjusting for age, race, year of publication, and survey methods, men were 1.37 (95% credible interval, 1.22 to 1.53) times more likely than women to have OAG. The prevalence of OAG was one third lower in studies in which routine visual fields were not assessed and that used an IOP criterion in the definition of glaucoma; this effect was reduced to the null after adjustment for age, racial group, and year of publication. CONCLUSIONS: Although black populations had the highest prevalence of OAG at all ages, white populations showed the steepest increase in OAG prevalence with age. Men were more likely than women to have OAG.