OBJECTIVES: To perform an analysis, from a public financing viewpoint, of the economic impact and efficiency of the Oncotype DX (ODX) assay as a guide to providing chemotherapy to women with early breast cancer compared to guiding this decision using the Adjuvant! Online (AO) prognostic index. METHODS: Markov model was constructed to assess three alternatives: provision of chemotherapy to women with a high risk recurrence score (RS) (i.e., >30) with ODX, to women with an intermediate/high risk score (RS >18) and to those as indicated by the AO. For the base case, a price of €3200 was set for ODX plus €236.12 for treatment with tamoxifen for 6 months, plus €3490.50 for six cycles of chemotherapy. RESULTS: Mean cost associated with AO to guide the provision of chemotherapy was €8994.02 per patient, with ODX RS >30 as a guide was €11,521.56, and for RS >18 it was €12,070.03.  The incremental cost effectiveness ratio for  ODX RS >30 compared to AO was €9659.28 per QALY; for ODX RS >18 was €7105.80.  When treatment was guided by AO, a mean of 16.80 QALYs were obtained per patient, ODX was associated with a mean 17.06 QALY with an RS of >30 and 17.13 QALY per with an RS of >18. In probablistic sensitivity analysis, assuming a willingness to pay of €10,000/QALY, providing chemotherapy to patients with an ODX RS of >18 became the best alternative. Probability of this being the best choice was 60% for a willingness to pay of €20,000 /QALY and 70% for €30,000 /QALY. CONCLUSIONS: Compared to guiding the provision of chemotherapy with AO, the ODX  would appear to be cost-effective. In the Spanish setting, for a willingness to pay €30,000/QALY, the best option would appear to be to prescribe chemotherapy for patients with ODX RS of >18.