The distribution of intraocular pressure (IOP) and the prevalence of glaucoma and their correlates were studied in a population-based study of inhabitants aged 70 years or older of three communities in the county of Oulu, Finland. 500 of the 560 eligible subjects (89%) were examined. IOP was measured using applanation tonometry. The diagnosis of glaucoma (or suspected glaucoma) was based on previous history and/or characteristic optic disc changes assessed first by ophthalmoscopy and later by photographic evaluation. No correlation existed between IOP level and age, but IOP was higher in women than in men. Glaucoma occurred in 12% of the participants (60 of 500 persons). In 42 of the 60 persons (8% of the participants) glaucoma had been diagnosed before this survey: non-exfoliative open-angle glaucoma in 15 persons (3.0%), bilateral or unilateral exfoliative open-angle glaucoma in 19 persons (3.8%), and congestive glaucoma in 8 persons (1.6%). In another 18 persons (4% of the participants) new open-angle glaucoma was detected, one third of these were exfoliative. In addition, 6% of the study population had suspected glaucomatous disc changes. In all new glaucoma cases and in all suspected cases the IOP was lower than 25 mmHg. Ocular hypertension (> or = 25 mmHg) without disc changes was found in 2%.