Seventeen patients with symmetrical stage 3 retinopathy of prematurity (ROP) and plus disease were assign to cryotherapy in one eye. Treatment was confined to the avascular zone of retina. Twelve treated eyes (71%) improved and 10 untreated eyes (59%) became worse. However, in only five patients did the treated eye improve and the untreated eye become worse, a number too small to be statistically significant.