This study aimed to describe the cohort profile of the Northern Ireland Cohort for the Longitudinal Study of Ageing (NICOLA) and to report the prevalence of, awareness of and associations with glaucoma. Using geographic stratification, a representative sample of non-institutionalised Northern Irish adults aged over 50 years was invited to participate. NICOLA participants underwent a Computer-Assisted Personal Interview (CAPI), a Self-Completion Questionnaire (SCQ) and a health assessment. The CAPI and SCQ collected comprehensive sociodemographic and health-related data. At the health assessment, participants underwent optic disc stereophotography, intraocular pressure (IOP) measurement using ocular response analyser (ORA), autorefraction, spectral domain optical coherence tomography and self-reported history of glaucoma. We invited NICOLA participants suspected of having glaucoma due to optic disc appearance or raised IOP for clinical examination by a glaucoma expert and perimetry. Epidemiological definitions by the International Society Geographical and Epidemiological Ophthalmology were used to define glaucoma. Of 3221 NICOLA participants (mean age 64.4, SD 8.5, female sex 51.7%) who attended the health assessment component of the NICOLA study (and had a vertical cup to disc ratio measurement in at least one eye), 91 participants had glaucoma. Overall, the crude prevalence of glaucoma was 2.83% (95% CI 2.31% to 3.46%) and 67% of affected individuals did not give a self-reported history of glaucoma. The prevalence of glaucoma in Northern Ireland is comparable with other population-based studies of European populations. Approximately two-thirds of people with glaucoma were undiagnosed. © Author(s) (or their employer(s)) 2020. No commercial re-use. See rights and permissions. Published by BMJ.