Cryotherapy for Retinopathy of Prematurity Cooperative Group Reports from the 3- and 12-month follow-up examinations in the Multicenter Cryotherapy for Retinopathy of Prematurity trial indicated a beneficial effect of cryotherapy in the treatment of severe retinopathy of prematurity. This report provides results from the 3 1/2-year follow-up examination on 92% of the 256 survivors from the original cohort of 291 infants in the randomized trial. Functional outcome was evaluated by masked assessment of letter acuity using the HOTV crowded letter test and grating acuity using the Teller Acuity Card procedure. Structural outcome was evaluated by physician's assessment of retinopathy of prematurity residua in the posterior pole. All three outcome measures showed a reduction in unfavorable outcomes in treated vs control eyes: 46.6% vs 57.5% (P < .01) for letter acuity, 52.4% vs 65.6% (P < .001) for grating acuity, and 26.1% vs 45.4% (P < .001) for posterior pole status. These results support the long-term efficacy and safety of cryotherapy in the treatment of severe retinopathy of prematurity.