Objective: To investigate the longitudinal changes in flicker perimetry in patients with age-related macular degeneration (AMD) as the condition progresses from early AMD to geographic atrophy (GA) or choroidal neovascularization (CNV). Methods: Patients with AMD and control subjects were recruited from a longitudinal study of retinal function in early AMD consisting of 187 participants. Only those who completed at least 4 consecutive, 6-monthly flicker perimetry tests were selected for this study. Study groups consisted of everyone who went on to develop GA (n=16) or CNV (n=5), controls (n=24), and the high-risk, early- AMD participants whose eyes did not progress to GA or CNV (drusen >125 μm; n=18). The flicker sensitivity was determined, and its rate of change during the 18 months before the clinical detection of late AMD was calculated. Results: Eyes that went on to develop GA or CNV had a significantly reduced mean (SD) flicker sensitivity in the months before clinical detection of GA (15.8[5.6] dB) or CNV (19.1 [3.8] dB) compared with control eyes (22.9[3.0] dB) (P<.001) and with eyes that did not progress to GA or CNV (21.4[3.4] dB) (P<.001). The rate of change in flicker sensitivity was significantly increased in GA eyes (-0.07 dB/mo) (P<.001) but not in CNVeyes (0.006 dB/mo) (P=.56) compared with the control eyes (-0.003 dB/mo). Conclusions: Flicker sensitivity is reduced in eyes that go on to develop late AMD. The rate of change in flicker sensitivities over time was particularly useful in predicting eyes and areas within the eye that subsequently develop GA.