Objective: To estimate the prevalence and risk factors of primary open-angle glaucoma (POAG) in an urban population and compare the same with that of our published rural population data in southern India. Design: Population-based cross-sectional study. Participants: Four thousand eight hundred subjects 40 years or older were selected using a multistage random cluster sampling procedure in Chennai city. Intervention: Three thousand eight hundred fifty (80.2%) subjects underwent a complete ophthalmic examination, including applanation tonometry, gonioscopy, pachymetry, optic disc photography, and automated perimetry. Main Outcome Measures: Glaucoma was diagnosed using the International Society of Geographical and Epidemiological Ophthalmology Classification. Results: The distribution of intraocular pressure (IOP) and vertical cup-to-disc ratio (VCDR) was obtained from the right eye of the 2532 subjects with normal suprathreshold visual fields. Mean IOP was 16.17±3.74 mmHg (97.5th and 99.5th percentiles, 24 mmHg and 30 mmHg). The mean VCDR was 0.43±0.17 (97.5th and 99.5th percentiles, 0.7 and 0.8). One hundred thirty-five (64 men, 71 women) subjects had POAG (3.51%; 95% confidence interval [CI], 3.04-4.0). Primary open-angle glaucoma subjects (58.4±11.3 years) were older (P<0.0001) than the study population (54.8±10.6 years). One hundred twenty-seven (94%) subjects were diagnosed to have POAG for the first time. Two subjects (1.5%) were bilaterally blind, and 3 (3.3%) were unilaterally blind due to POAG. The urban population prevalence was more than that of the rural population (1.62%; 95% CI, 1.4%-1.8%; P<0.0001). In both populations, increasing IOP (per millimeter of mercury) and older age were associated with the disease. There was no association with gender, myopia, systemic hypertension, diabetes, or central corneal thickness. Conclusions: The prevalence of POAG in a ≥40-year-old south Indian urban population was 3.51%, higher than that of the rural population. The prevalence increased with age, and >90% were not aware of the disease.