OBJECTIVES: Anxiety disorders have been estimated to cost $46.6 billion annually in the United States. Social Anxiety Disorder (SAD) is among the most prevalent and most chronic of the anxiety disorders, but there is a lack of information on its economic impact. SSRIs have been proven to be effective in the prevention of relapse but further cost-effectiveness studies are required. This study evaluated the cost-effectiveness of escitalopram in comparison with placebo in relapse prevention of SAD. METHODS: The clinical study was conducted in outpatients (18-80 years) with a primary diagnosis of generalised SAD (DSM-IV) and an LSAS score ³70. After 12 weeks of open-label treatment (10-20mg/day escitalopram), responders were randomised to 24 weeks of escitalopram (n=190) or placebo (n=181) treatment, to assess the relapse rate. In addition to clinical evaluations, quality of life (SF-36) was assessed at baseline, and at Weeks 12 and 24 of treatment. The use of medical services and absence from work were recorded for the calculation of direct and indirect costs from the perspective of society. RESULTS: Patients treated with escitalopram experienced a better quality of life compared to placebo-treated patients (better scores for all the mental health-related dimensions: social functioning, role emotional, mental health; p<0.05, and vitality, p<0.10) and experienced fewer relapses. (The cumulative relapse rate at Week 24 was 23% for the escitalopram group versus 56% for the placebo group.) Total costs were 22.5% lower for patients treated with escitalopram compared to placebo (€255 versus €329; difference not statistically significant at the 5% confidence level). Relapse appears to be an important cost driver. CONCLUSIONS: Thus, continuation of escitalopram treatment is effective in the prevention of relapse in SAD patients. Escitalopram is more cost-effective than placebo and the drug purchase costs are more than offset by a decrease in total costs.