<b><i>Background:</i></b> Prophylactic indomethacin reduces the risk of severe intraventricular hemorrhage (IVH) but does not reduce death or neurodevelopmental impairment (NDI) among extremely low birth weight (ELBW) infants. Some investigators have suggested that prophylactic indomethacin may have a greater treatment effect on severe IVH among infants at high risk for severe IVH. <b><i>Objective:</i></b> To determine whether the relative treatment effects of prophylactic indomethacin on severe IVH and the composite outcome of death or NDI vary based on the risk of severe IVH. <b><i>Methods:</i></b> Post hoc analysis of the Trial of Indomethacin Prophylaxis in Preterms (TIPP). We generated a model to predict the risk for severe IVH based on gestational age, birth weight, antenatal steroids, delivery mode, outborn status, sex, and 5-min Apgar score, and we divided the TIPP participants into risk quartiles. We used logistic regression to determine the adjusted odds ratios (aOR) of severe IVH and death or NDI based on indomethacin treatment for each quartile. <b><i>Results:</i></b> The relative treatment effects of prophylactic indomethacin on severe IVH did not vary based on the predicted risk of severe IVH: quartile 1: aOR 0.68 (95% confidence interval [CI] 0.19-2.37); quartile 2: aOR 0.61 (95% CI 0.27-1.42); quartile 3: aOR 0.63 (95% CI 0.31-1.31); quartile 4: aOR 0.58 (95% CI 0.32-1.05). The relative treatment effect of prophylactic indomethacin on death or NDI did not vary significantly between quartiles. <b><i>Conclusions:</i></b> These findings do not support selective prophylactic indomethacin treatment to improve long-term outcomes of ELBW infants at high risk for severe IVH.