OBJECTIVES: Social Anxiety Disorder (SAD) is a chronic disabling psychiatric disorder. SSRIs are recognized as effective first-line treatment, but relapse rates as high as 60% have been reported when treatment is discontinued. Inappropriate treatment of this condition places significant economic burdens upon society. The aim of this study was to compare costs and the impact on quality of life of relapsed SAD patients with a control group of non-relapsed patients. METHODS: An economic evaluation conducted alongside a double-blind, placebo-controlled, 9-month relapse prevention clinical study was used to compare the quality of life and costs for relapsed and non-relapsed patients. Relapse was either an increase of the Liebowitz Social Anxiety Scale (LSAS) total score of at least 10 points or as judged by the clinician. Quality of life assessments (SF-36) were made at baseline, and at weeks 12 and 24 of treatment. Medical services usage and sick leave days were calculated from the societal perspective. RESULTS: At the end of the 6-months, 133 patients had relapsed and 238 were still in remission. Total costs at endpoint were higher for relapsed patients compared to non-relapsed patients (€337 versus €265). Sick leave was the main cost driver. The likelihood of needing sick leave was 14% and 7% for relapsed and non-relapsed patients, respectively (p=0.047) with fewer days of sick leave for non-relapsed patients. Relapsed patients had a poorer quality of life compared to non-relapsed patients (lower scores for all the mental health related dimensions: social functioning, role emotional, mental health and vitality; p <0.001). CONCLUSIONS: Relapsed patients have a poorer quality of life and incur higher costs. This highlights the need for drugs that are effective in preventing relapse in SAD patients.