This study investigated the severity of retinopathy of prematurity (ROP) and its relationship to childhood development. The subjects were 21 children with a birthweight of 2500 g or less who were tested for flash visual evoked potential (FVEP) at conceptual ages ranging from 1 to 3 years. We also examined 73 children with a birthweight of 1500 g or less, using the Developmental Quotient (DQ) test, at 2 1/2 years of age. Twenty-five of this group were given an Intelligence Quotient (IQ) test at 6 to 7 years of age. The P100 latency of FVEP in the severe ROP group was significantly longer than that of the mild ROP group (P < 0.05). The main DQ in the severe ROP group was 99.1 +/- 17.9, significantly lower than the 108.7 +/- 15.5 of the mild ROP group (P < 0.05). No significant IQ differences were found between the two groups. The proportion of children with verbal-performance IQ discrepancies was, however, significantly greater in the severe ROP group than in the mild ROP group (P < 0.05). Since infants with severe ROP are more likely to suffer developmental disorders, long-term follow-up is absolutely necessary and must be done in cooperation with pediatricians.