Retinopathy of prematurity is a disease of developing blood vessels. Although it is seen predominantly in premature infants requiring life support systems to survive, it does occur in full-term infants, infants with hypoxia, cyanotic heart disease and in stillborn infants. Although oxygen has been considered to be the prime aetiologic agent, evidence for this, particularly in recent years, is not compelling. The timing of the occurrence of the disease is closely related to the conceptional age of the infant rather than weeks post birth, birth weight, gestational age at birth. In addition, the case to case similarity of the disease, as well as the diverse cell types produced in unfavourable outcomes (cicatricial ROP), point to the possibility of an in utero insult to the clone of cells giving rise to the vascular endothelium providing blood supply to the neural retina.