Objective To test the hypothesis that administration of indomethacin prophylaxis before 6 hours of life results in a lower incidence of intraventricular hemorrhage (IVH) compared with administration after 6 hours of life, and that the effects of early prophylaxis depend on gestational age (GA) and sex in very low birth weight infants (birth weight <1250 g). Study design Very low birth weight infants admitted to our neonatal intensive care unit between 2003 and 2010 who received indomethacin prophylaxis were analyzed retrospectively. Exclusion criteria included unknown time of indomethacin prophylaxis, death at <12 hours of life, congenital anomalies, and unavailable head ultrasound report. Infants were dichotomized based on the timing of indomethacin prophylaxis (<6 hours or >6 hours of life) to compare incidence of IVH all grades and severe (grade 3-4) IVH. Secondary analyses examined the effects of the time of indomethacin prophylaxis initiation by GA and sex on the incidence of IVH. Results A total of 868 infants (431 males and 437 females) met the criteria for analysis. Indomethacin prophylaxis was given at <6 hours of life in 730 infants and at >6 hours of life to 168 infants. The 2 groups differed with respect to antenatal steroid exposure, GA, outborn prevalence, and pneumothoraces. After multivariate analysis, there were no between-group differences in all-grade or severe IVH. However, females, but not males, treated at <6 hours of life had a lower incidence of severe IVH (P < .05), particularly at lower GAs. Conclusion Prophylactic indomethacin administered before 6 hours of life is not associated with lower incidence of IVH.