OBJECTIVES: To estimate the expected value of perfect information (EVPI) associated with a lifetime Markov-model which evaluated the cost-effectiveness of rivaroxaban and dabigatran compared to enoxaparin for venous thromboembolism (VTE) prophylaxis after total hip replacement (THR). To estimate the expected value of perfect parameter information (EVPPI).  To indentify the model parameter subset whose uncertainty drives the decision uncertainty.  To decrease the uncertainty, by collecting additional data on this subset. To investigate the impact of threshold change on the EVPI/EVPPI values. METHODS: EVPI was determined directly from PSA and was calculated over the threshold €0-100,000/QALY. Population EVPI (PEVPI) was calculated based on the 5464 THR procedures performed in Ireland in 2006 and the ENDORSE-study which revealed that 64% of at risk surgical patients in Ireland receive recommended VTE prophylaxis. The assumptions were; a 50% policy of choice uptake rate, a 4% discount rate and a 10-year time horizon.  Alternative assumptions of 5 and 15 years were explored. EVPPI were calculated for the 3 parameter subsets using the 2-stage Monte-Carlo algorithm. RESULTS: Base-case analysis indicated that rivaroxaban dominated.  Probabilistic analysis (PSA) indicated that at €45,000/QALY, the probability that rivaroxaban was the most cost-effective strategy was 67%. The PEVPI was €15.62 million.  Costs had the highest EVPPI (€12.43 million), followed by probabilities (€1.45 million) and preference weights (€1.44 million). The costs subset was most sensitive to threshold. Costs were updated with a more detailed costing study.  All analyses were repeated. Base-case analysis indicated that rivaroxaban continued to dominate. The probability that rivaroxaban was the most cost-effective strategy increased to 81%. PEVPI decreased to €4.59 million. EVPPI for costs decreased to €2.13 million. EVPPI for probabilities and preference weights were €1.03 million and €0.94 million respectively. CONCLUSIONS:   This study demonstrates the application of EVPI/EVPPI analyses to quantify and decrease uncertainty associated with the choice of VTE prophylaxis after THR in the Irish health care setting.