Early detection of retinopathy of prematurity (ROP) in premature and very-low-birth-weight infants is crucial. In this retrospective study, 581 infants either with a birth weight below 1500 g or a gestational age of less than 32 weeks, or who did not fit these criteria but were judged to be at increased risk, were screened for ROP. ROP developed in 159 (27.4%). The incidence of ROP appeared to be inversely proportional to birth weight and gestational age. Infants with a birth weight below 750 g had a significantly higher risk of developing stage 3 and 4 ROP. The mean age at detection was 7.6 +/- 1.6 weeks. Nearly all of the ROP cases and all of the stage 3 and 4 cases were detected between the 5th and 10th week. Because screening should be focused on these vision-threatening stages, ophthalmic examinations should be concentrated in, but not limited to, the period between the 5th and the 10th postnatal week.