OBJECTIVES: Atomoxetine is the first medication to receive marketing authorization in Spain for the treatment of newly diagnosed adults with Attention-Deficit/Hyperactivity Disorder (ADHD). The aim of this analysis was to assess if treatment with atomoxetine in adults with ADHD was cost-effective vs. placebo from the Spanish Healthcare System perspective. METHODS: A Markov state transition model was developed for a theoretical cohort of newly diagnosed adult patients with moderate-severe ADHD.  Key input data (response and discontinuation) were derived from the atomoxetine trial program. Patients enter the model at the age of 18 and receive atomoxetine (initiated at 40mg for a week and then titrated to 80mg or 100mg) or placebo (in the absence of another authorized medication for the treatment of newly diagnosed adults with ADHD). Treatment success has been defined as response to treatment, showing improvements in both symptoms and functioning as measured by the CAARS and CGI-S scales, respectively. Treatment, non-specific health state utilities were populated with estimates from a vignette study in adults conducted in the UK. Drug and direct medical costs were obtained from local databases.  In accordance with other published ADHD models, a 1-year time horizon was used. To check the model for robustness, probabilistic and deterministic sensitivity analyses were performed. RESULTS: Atomoxetine was found to be cost-effective with an ICER of €24,248/QALY despite patients in placebo arm only accumulating cost of physician visits. In addition, a QALY gain of 0.023 was projected, due to greater proportion of patients responding to treatment in the atomoxetine arm. Results from a probabilistic sensitivity analysis indicated that atomoxetine has a 57% probability of being more cost-effective than placebo at a willingness to pay threshold of €30,000/QALY in the Spanish setting. CONCLUSIONS: Atomoxetine is a cost-effective option versus no active medical treatment for newly diagnosed adults with ADHD in Spain.