Neovascular membranes that lie under the geometric center of the foveal avascular zone are larger than neovascular membranes completely outside the foveal avascular zone. Thirty-eight (66%) of 58 subfoveal membranes were greater than 1500 microns in diameter while only seven (12%) of 58 extrafoveal membranes were greater than 1500 microns (P<.000001). Of all eyes with subfoveal membranes and an initial visual acuity of 20/100 or better.acuity remained the same or improved in 5 (38%) of 13 eyes with small membranes and in none (0%) of 13 eyes with large membranes (P<0.02) after an average follow-up of 22 months. Furthermore, nine (70%) of the 13 eyes with large membranes and an initial visual acuity of 20/100 or better were 20/200 or worse at follow-up. For eyes whose initial visual acuity was 20/126 or worse, a statistically significant difference could not be demonstrated in the visual prognosis between eyes with small vs large membranes. Nevertheless, all but one of these eyes remained 20/126 or worse at follow-up, including 80% that were 20/200 or worse at follow-up regardless of membrane size. Because of the uniformly poor visual prognosis for eyes with large subfoveal membranes, a randomized trial of krypton red photocoagulation seems justifiable if careful low-vision assessments are done before and after the trial.