We have investigated the incidence of retinopathy of prematurity (ROP) among premature infants with birth weight less than 1500 g in two Norwegian counties during the years 1989-1993. Two hundred and seven out of 244 such infants (84.8%) were examined at the neonatal intensive care unit; 66 of those examined (31.9%) had a birth weight below 1000 g. ROP was found in 21 patients (10.1%), and stage 3 disease was present in 7 (3.4%). No patient had more advanced ROP than stage 3. Assuming that no cases of stage 3 ROP were missed among the total of 244 children, the incidence of stage 3 disease was 2.9%. The frequency of ROP in this study is compared to that of other population-based studies in the Nordic countries, and incidence differences are discussed.