Objective:To determine the incremental cost-effectiveness of indomethacin pr ophylaxis in extremely lowbirth weight infants enrolled in the Trial of Indometh acin Prophylaxis in Preterms(TIPP).Study design:Participants in this economic evaluation were 428 infants enrolled at 9 Canadian TIPP centres.The study took a third-party payer perspective.Prior to the analysis of clinical trial data,direct medical costs were derived from chart review of 89 items of resource uti lization,for each day from admission to hospital discharge.Unit costs for each resource were obtained from a provincially standardized costaccounting system.Incremental cost-effectiveness analysiswas performed,with estimation of cost-effectiveness acceptability curves through non-parametric bootstrapping.Result s:The mean(SD)cost was ＄68 279(40 317)for the placebo group and ＄69 629(37 989)for the indomethacin group.Indomethacin prophylaxis cost an additional ＄67 500 per death or impairment averted.However,the precision of this estimat e was low,such that the probability that the estimate was lower than ＄300 000 per death or impairment averted was only 61%.The results were similar when sur gical costs were assumed to be 500%of those measured in the trial.Conclusions:This study does not provide an economic rationale for the use of indomethacin p rophylaxis in ELBW infants. Objective: To determine the incremental cost-effectiveness of indomethacin pr ophylaxis in extremely lowbirth weight infants enrolled in the Trial of Indometh acin Prophylaxis in Preterms (TIPP). Study design: Participants in this economic evaluation were 428 infants enrolled at 9 Canadian TIPP centers. The study took a third-party payer perspective. Prior to the analysis of clinical trial data, direct medical costs were derived from chart review of 89 items of resource uti lization, for each day from admission to hospital discharge. Unit costs for each resource were obtained from a provincially standardized costaccounting system. incremental cost-effectiveness analysiswas performed, with estimation of cost-effectiveness acceptability curves through non-parametric bootstrapping. Results s: The mean (SD) cost was $ 68,279 (40,317) for the placebo group and $ 69 629 (37 989) for the indomethacin group. Indomethacin prophylaxis cost an additional $ 67 500 per death or impairment averted. However, the precisi on of this estimat e was low, such that the probability that the estimate was lower than $ 300 000 per death or impairment averted was only 61%. The results were similar when sur gical costs were assigned to be 500% of those measured in the trial.Conclusions: This study does not provide an economic rationale for the use of indomethacin p rophylaxis in ELBW infants.