OBJECTIVES: Clinical studies have highlighted the high risk of recurrence following complete resection of primary GIST. Published data from the phase III (ACOSOG Z9001) trial have demonstrated significant clinical benefit with adjuvant imatinib vs. placebo with respect to recurrence-free survival (RFS 98% vs. 83% at 1 year). We conducted a health economic evaluation for imatinib as adjuvant therapy for GIST that can be used to support this indication. METHODS: A Markov model was used to project lifetime outcomes and costs for patients who undergo complete gross resection of primary GIST. Cost-effectiveness was measured in terms of the incremental cost per quality adjusted life year (QALY) gained with the addition of imatinib. Probabilities of disease recurrence, resource use, utilities and costs were derived from ACOSOG Z9001 trial and other secondary sources. Results were generated under three scenarios regarding the treatment duration with imatinib: 1-year, 3-year and continuous treatment with imatinib. RESULTS: Adding imatinib was projected to result in a gain of 0.745, 1.538 and 5.180 QALYs assuming 1-year, 3-year and continuous treatment scenarios, respectively. These clinical benefits of imatinib are obtained at an additional expected per-patient lifetime cost of $30,042, $81,125 and $345,360 assuming 1-year, 3-year and continuous treatment scenarios, respectively. The incremental cost per QALY gained with imatinib was therefore $40,328, $52,760 and $66,669 assuming 1-year, 3-year and continuous treatment scenarios, respectively. Deterministic sensitivity analyses showed the results to be robust with respect to variations in assumptions and estimates. The probability that imatinib is cost-effective given a threshold value of $100,000 per QALY was over 98% in all scenarios. CONCLUSIONS: Results of this evaluation suggest that, from a Canadian health care system perspective, imatinib is cost-effective and represents good value for the money according to currently accepted standards of cost-effectiveness.