PURPOSE To explore the association between peripapillary atrophy (PPA) area and conversion from ocular hypertension (OHT) to glaucoma. DESIGN Prospective, longitudinal cohort study of cases and controls. PARTICIPANTS We included 279 age-matched and follow-up time-matched eyes with OHT that converted to glaucoma and 279 eyes with OHT that did not convert to glaucoma. METHODS Initial and last acceptable optic disc photos were analyzed. Disc, α-zone, and β-zone PPA were traced independently by 2 trained readers and their areas were measured with Photoshop. The α-zone and β-zone areas were expressed as a percentage of optic disc area. MAIN OUTCOME MEASURES α-Zone and β-zone PPA size over time. RESULTS Intraclass correlation coefficients (ICCs) demonstrated that readers had good agreement on disc area (ICC = 0.97) and β-zone (ICC = 0.82), but not α-zone (ICC = 0.48). The ß-zone, as a percentage of disc area, increased in size (P < 0.001) in both eyes with incident primary open-angle glaucoma (mean, 10.6%; standard deviation, 22.6%) and matched controls (mean, 10.1%; standard deviation, 33.7) over follow-up (mean, 12.3 years). The increase in size did not differ between cases and controls (P = 0.82). Enlargement of the β-zone was not correlated with follow-up time (P = 0.39). CONCLUSIONS The results did not show a difference in size of the β-zone at baseline between eyes that proceed to develop glaucoma and those that do not. Moreover, the β-zone enlarges equally in case and control eyes during follow-up.