ObjectivesTo investigate inter-reader agreement on five severity levels of central vascular changes (none, mild, moderate, severe pre-plus disease, plus disease) and aggressive posterior retinopathy of prematurity (ROP), and to see whether an unintended shift in indication for treatment occurred.MethodsFour international ROP readers participated. Before the grading of the photographs, the readers were informed that a high proportion of advanced ROP cases were included. In total, 243 photographs/948 quadrants were available from 136 infants. As a standard series of photographs was available, grading was performed under optimised conditions.ResultsThe four readers agreed on the quadrant scores of only 70 (7.38%) of the 948 quadrants-that is, on 1, 5, 15, 4 and 45 quadrants for scores 0, 1, 2, 3 and 4, respectively. The mean scores differed systematically between the readers (permutation test, p