PURPOSE: The clinical usefulness of subcutaneous allergen immunotherapy (SCIT) in the treatment of atopic dermatitis (AD) is still controversial. We analyzed the clinical efficacy of SCIT in patients with AD and the clinical characteristics of patients showing a favorable clinical response to the treatment. MATERIALS AND METHODS: Two hundred and fifty one patients with AD sensitized to house dust mite (HDM) were treated by SCIT using HDM extract. The clinical severity of AD was measured using the standardized clinical severity scoring system for AD (SCORAD) at baseline and 12 months. A favorable clinical response to SCIT was defined as a decrease in SCORAD value at 12 months greater than 50% compared to baseline value. Severe AD was defined as a baseline SCORAD value above 50. RESULTS: A favorable clinical response to SCIT was observed in 73.6% of patients. The proportion of patients showing a favorable clinical response to SCIT was significantly higher in patients with severe AD (90.6%) than patients with mild to moderated AD (63.7%) (p<0.001). Patients with severe AD showing a favorable clinical response had a significantly shorter duration of AD (12.3+/-8.5 years: mean+/-SD) than patients with severe AD showing no significant clinical response (20.6+/-10.9 years) (p<0.05) at baseline. CONCLUSION: SCIT could be a clinically useful therapeutic option for patients with severe AD sensitized to HDM. Early initiation of SCIT might provide a favorable clinical outcome in patients with severe AD sensitized to HDM.