To determine the percentage of Medicare beneficiaries with primary open-angle glaucoma (POAG) treated medically or surgically, utilization rates for each major class of glaucoma medication, and factors influencing treatment. Longitudinal observational study using data from the Medicare Current Beneficiary Survey (MCBS). Persons age 65 and older with POAG, 1992 to 2002 (N = 6446). By using MCBS data merged with Medicare claims, rates of medical and surgical treatment for participants with POAG were determined. Logistic analysis was used to assess factors associated with use of care. Receipt/nonreceipt of medical or surgical therapy in a year and rates of drug utilization by class and of surgery by type among persons who did not receive medical therapy in a year. On average from 1992 to 2002, 27.4% of persons diagnosed with POAG received no medical or surgical treatment. Rates of nonuse increased by 3% annually (odds ratio [OR], 1.03; 95% confidence interval [CI], 1.02-1.05). Beneficiaries with Medicaid were 43% more likely not to receive care for POAG in a year (OR, 1.43; 95% CI, 1.20-1.70). Hispanic, Asian, and beneficiaries of other race/ethnicity were less likely to receive treatment than were whites. Use of beta-blockers and miotics decreased, but utilization rates increased substantially for alpha-agonists, combination beta-blocker-carbonic anhydrase inhibitors, and especially prostaglandin analogs. Despite availability of more efficacious glaucoma medication classes with few side effects and findings of clinical trials underscoring the importance of intraocular pressure reduction in POAG patients, many patients with POAG continue to go untreated.