The purpose of this article is to update the International Classification of Retinopathy of Prematurity (ICROP) using the evidence base that has accumulated since its first publication in 1984.1 This document is the consensus of a group of 15 ophthalmologists from 6 countries, several of whom were members of the original ICROP committees from the early 1980s and all of whom have extensive clinical experience with this disorder. The original ICROP, described first in a 1984 publication1 and expanded in 1987,2 has provided a basis on which numerous treatment trials and observational studies of this potentially devastating disorder could be undertaken. The original ICROP dealt with the early phases of the disorder and was based on several key observations essential in describing the retinopathy. These include (1) the location of retinal involvement by zone, (2) the extent of retinal involvement by clock hour, (3) the stage or severity of retinopathy at the junction of the vascularized and avascular retina, and (4) the presence or absence of dilated and tortuous posterior pole vessels (plus disease). The revision proposed herein has adhered to the original descriptive nature of the disease, and the committee has not attempted to explain the mechanism of the disease. However, improved retinal imaging techniques allow capturing images of a quality that was unimagined at the time of the initial classification and, thus, the developing retinopathy can be examined by several observers without endangering the tiny infant.