For a four-year period the development of retinopathy of prematurity (ROP) was determined among neonates considered at risk of acquiring this condition. Fifty-six out of 249 premature infants developed some degree of ROP. Comparison of these infants with a group of 56 controls, admitted to hospital in the same period and matched for sex, birth weight, and gestational age, showed significant differences for sepsis, blood transfusions, and the period of oxygen monitoring in relation to the period of oxygen administration. The most consistent factor associated with the development of ROP was gestational age at the time of birth, though no gestational age group was entirely devoid of ROP. This suggests that screening for ROP should not be restricted to high-risk premature infants only.