OBJECTIVES: Glaucoma is an ocular disease resulting in irreversible loss of visual function. Early identification and treatment has been demonstrated to improve outcomes, but incurs additional costs. This analysis was performed to determine the incremental cost-effectiveness of early compared to late treatment of patients with Primary Open Angle Glaucoma (POAG). METHODS: A decision analytic Markov model was developed using a 25-year time horizon. The perspective was that of the Ministry of Health and Long-term Care of Ontario, Canada; thus, included only direct medical costs. Health states were defined according to mean visual field deviation scores as mild (0 to - 4.9), moderate (-5.0 to -11.9), severe (-12 to -19.9), and legally blind (-20+). The primary outcome was defined as vision years gained (VYG), i.e., time prior to reaching the legally blind (absorbing) state. Costs and outcomes were derived from the literature; expert opinion was consulted where necessary. All costs are reported in 2005 Canadian dollars. All costs and outcomes were discounted at a 5% rate. The pharmacoeconomic outcome was incremental cost per VYG. Various one-way and multi-variable probabilistic sensitivity analyses were performed to test the robustness of the results. RESULTS: Total discounted costs of early and late treatment were $7107 and $5608, respectively. Differences in costs were attributed to an increased need for resource intensive procedures and physician visits, approximately 75% of the total cost of the severe and legally blind health states. Total expected VYG were 13.07 for early treatment and 12.65 for late treatment. The incremental cost effectiveness ratio was $3,543/VYG. Results were sensitive to decreases in the rate of disease progression and time horizon and increases in the yearly cost of treating patients with mild disease. CONCLUSIONS: Early treatment of patients diagnosed with POAG is a reasonably cost-effective choice, providing added years of vision.