Abstract: BACKGROUND: Postnatal exposure to red blood cell transfusion (RBCT) in premature infants is an important risk factor for Retinopathy of Prematurity (ROP) progression. We hypothesized that higher number and earlier timing of RBCT are associated with worse ROP severity and result in laser treatment at an earlier postmenstrual age (PMA) in very low birth weight (≤1500 g, VLBW) infants. METHODS:A retrospective medical record review of 631 VLBW infants over a 5-year period was performed. Demographic features and potential clinical risk factors including number of RBCT, ROP severity, and progression to laser treatment were collected to evaluate predictors of severe ROP. ANCOVA, pairwise post-hoc analyses, and multivariate regression were used to determine associations between frequency and timing of RBCT and ROP severity. RESULTS: Of the 456 eligible infants, 61 developed severe ROP (13%). There was significant correlation between number of RBCTs and ROP severity, adjusted for gestational age and birthweight (Adjusted R2 = 0.53; p < 0.001). Compared to infants with No/Mild and Type 2 ROP, infants with Type 1 ROP received more RBCTs, with higher number of RBCTs per week during the first month of life (mean RBCT in ROP No/Mild 5.7±0.4 vs Type 2 16.3±1.8 vs Type 1 22.4±1.5, p = 0.042). Laser-treated infants received a higher number of RBCTs than non-treated infants (mean RBCT 22.3 vs. 6.5, p < 0.001) but no correlation was observed between number of RBCTs and PMA at time of laser treatment. CONCLUSION: Higher number of RBCTs in early postnatal life of VLBW infants was associated with more severe ROP.