OBJECTIVE: To describe characteristics of the Age-Related Eye Disease Study (AREDS) 9-step severity scale applied to participants in the Complications of Age-related Macular Degeneration Prevention Trial (CAPT). METHODS: Eligibility criteria for CAPT required 10 or more large (>or=125 microm) drusen in each eye. Readers graded baseline photographs from all participants and all follow-up photographs from 402 untreated eyes. Drusen and pigment characteristics were used to assign the AREDS scale score. Choroidal neovascularization was identified from fluorescein angiograms. Geographic atrophy involving the macular center was identified from color photographs. RESULTS: Among 1001 untreated eyes, 90% were at steps 5 to 7 at baseline. The 5-year incidence of advanced age-related macular degeneration (AMD) increased with each step from 8% (step 4) to 40% (steps 8 and 9 combined). These rates were similar to those reported in AREDS. Among 261 eyes with all 5 annual photograph gradings available and without progression to advanced AMD, 55% of eyes had scores that indicated improvement at least once. Before progression to advanced AMD, only 32% of 141 eyes either went through step 8 or 9 or had an increase of 2 or more steps from baseline. CONCLUSIONS: The AREDS 9-step severity scale was predictive of development of advanced AMD. The AREDS scale has deficiencies as a surrogate outcome for progression to advanced AMD.