Certain general conclusions can be drawn from a series of 56 studies on glaucoma prevalence. Even in the most recently published studies the rate of undiagnosed glaucoma is particularly high. Another fairly constant finding is the discrepancy between the clinical and epidemiologic diagnoses of glaucoma. The prevalence of primary open-angle glaucoma (POAG) has been increasing, and this trend is undoubtedly due at least in part to advances in diagnostic technology. The decreasing prevalence of primary angle-closure glaucoma (PACG) is due to the adoption of more stringent criteria for the diagnosis of this form of glaucoma. Prevalence increases proportionately with age for each racial group. African or African origin populations had the highest POAG prevalence at all ages but the increase in prevalence of POAG is steeper for white populations. PACG is commonest in Asian ethnic groups, with the exception of the Japanese. Low-tension glaucoma (LTG) is quite common in the Japanese population. Over 80% of those with PACG live in Asia, while POAG disproportionately affects those of African derivation. Women are more affected by glaucoma. Very few incidence studies have been completed, because the cost of examining large samples is high. There are only two recent studies conducted on persons of African descent in Barbados (West Indies) and on white inhabitants of Rotterdam (Netherlands). Risk of incident glaucoma was highest among persons classified as having suspect POAG at baseline, followed by those with ocular hypertension. No difference in incidence of POAG between men and women was found. The more recent studies which included routine visual-field testing reveal rates of blinding glaucoma <10% in many countries, including those that are developing.