Purpose: To determine the incidence of open-angle glaucoma (OAG) in Melbourne, Victoria, Australia. Design: Population-based cohort study. Participants: Total of 3271 participants aged 40 years and older from Melbourne, Victoria, Australia. Main Outcome Measures: Five-year incidence of OAG. Methods: Participants were recruited through a cluster random sampling from nine urban clusters. Baseline examination was conducted from 1992 through 1994, and the follow-up data were collected from 1997 through 1999. Each participant both at baseline and follow-up underwent a standardized ophthalmic examination including intraocular pressure measurement, visual field assessment, cup-to-disc ratio measurement, and paired stereo photographs of the optic disc. Glaucoma was assessed by a consensus group of six ophthalmologists that included two glaucoma specialists. Glaucoma was diagnosed as possible, probable, or definite. Results: The overall incidence of definite OAG was 0.5% (95% confidence limits [CL], 0.3, 0.7); probable and definite incidence of OAG was 1.1% (95% CL, 0.8,1.4); and possible, probable, and definite OAG incidence was 2.7% (95% CL, 1.8, 3.7). The incidence of possible, probable, and definite OAG increases significantly as age increases (P < 0.001). The incidence of definite OAG increases from 0% of participants aged 40 to 49 years to 4.1% of participants aged 80 years and older. The incidence of probable and definite OAG increases from 0.2% of participants aged 40 to 49 years to 5.4% of participants aged 80 years and older. The incidence of possible, probable, and definite OAG increases from 0.5% of participants aged 40 to 49 years to 11% of participants aged 80 years and older. A nonsignificant but higher incidence of definite OAG among men was observed in this study when compared with women (odds ratio, 2.2; 95% CL, 0.9, 5.9). Fifty percent of the definite OAG participants were undiagnosed. Conclusions: The incidence of OAG increases significantly with age. The undiagnosed cases suggest the need to develop novel community screening strategies for glaucoma.