Purposes: To analyze the low weight gain (WG) from birth to the sixth week of life as a risk factor for retinopathy of prematurity (ROP). Methods: A prospective cohort study comparing incidence of ROP and WG after preterm birth. Were included infants with birth weight (BW) ?1,500 grams and gestational age ?32 weeks at birth. Main clinical outcome were development of any stage and severe ROP. Main variable was the proportion of WG to the BW at the sixth week of life. Prevalence of ROP was determined and chi-square and Student-t test were used to compare data. Logistic regression was performed and the accuracy of WG for the development of ROP were evaluated by receiver operating characteristic (ROC) curves. Results: Of 317 studied preterms, 98 (30.9%) developed ROP in any stage. Adjusted logistic regression in Group 1 indicated 1.055 OR for ROP (P<0.001) and Group 2, 1.031 (P=0.007). The area under the ROC curve for any stage ROP was 0.67% (P...