Background: Opioid addiction is a worldwide problem. Agonist opioid treatment (AOT) is the most widespread and frequent pharmacotherapeutic approach. Methadone has been the most widely used AOT, but buprenorphine, a partial kappa-opiod agonist and a my-opiod antagonist, is fast gaining acceptance. The objective was to assess the budgetary impact in Spain of the introduction of buprenorphine-naloxone (B/N) combination. Methods: A budgetary impact model was developed to estimate healthcare costs of the addition of B/N combination to the therapeutic arsenal for treating opioid dependent patients, during a 3-year period under the National Health System perspective. Inputs for the model were obtained from the specialized scientific literature. Detailed information concerning resource consumption (drug cost, logistics, dispensing, medical, psychiatry and pharmacy supervision, counselling and laboratory test) was obtained from a local expert panel. Costs are expressed in euros (, 2010). Results: The number of patients estimated to be prescribed B/N combination was 2,334; 2,993 and 3,589 in the first, second and third year respectively. Total budget is 85,766,129; 79,855,471 and 79,137,502 in the first, second and third year for the scenario without B/N combination. With B/N combination the total budget would be 86,589,210; 80,398,259 and 79,708,964 in the first, second and third year of the analyses. Incremental cost/ patient comparing the addition of the B/N combination to the scenario only with methadone is 10.58; 6.98 and 7.34 in the first, second and third year respectively. Conclusion: Addition of B/N combination would imply a maximum incremental yearly cost of 10.58 per patient compared to scenario only with methadone and would provide additional benefits.