Twenty-eight patients with bilateral symmetrical Stage 3 retinopathy of prematurity (ROP) and plus disease had one eye assigned to cryotherapy and the other to control. The majority of patients weighed under 1000 grams at birth and females outnumbered males by nearly a two-to-one ratio.+ Cryotherapy was generally performed at a gestational age of less than 40 weeks and a mean chronologic age of 10 weeks. Eleven patients showed improvement in both the treated and untreated eyes possibly due to variables among prematures not identified in the study. Eleven other patients experienced improvement in the treated eye and progression in the untreated eye. Using the binomial distribution on the latter group the P value was 0.0005 with a one-tailed hypothesis test and 0.001 with a two-tailed test, suggesting that in the sampled population cryotherapy appears to be preferred over no treatment.