The interobserver and intraobserver reliability in determining clinical characteristics of drusen were measured in 161 eyes with age-related macular degeneration (AMD). The percent agreement was 76% for the number of drusen; 89% for the presence or absence of soft drusen; 79% for the presence or absence of confluence drusen; 84% for the presence or absence of focal hyperpigmentation; and, 91% for the presence or absence of geographic (areolar) atrophy. Kappa for each of these characteristics ranged from 0.46 to 0.71 in eyes of patients with bilateral nonexudative AMD and from 0.59 to 0.80 in the fellow eye of patients with unilateral exudative AMD (disciform scarring or macular changes associated with choroidal neovascularization). A significant difference could not be shown in the interobserver reliability for each drusen characteristic after stratifying the data into eyes from patients with bilateral drusen and patients with unilateral exudative AMD. The intraobserver reliability for two graders, obtained on approximately 30% of the original study group by repeating these gradings 6 months after the initial gradings, ranged from 85% to 96% with kappas from 0.60 to 0.85 for all drusen characteristics except for number of drusen. These readers demonstrated good interobserver and intraobserver agreement using definitions describing each of these drusen characteristics.