BACKGROUND Very few studies have evaluated the effects of sublingual immunotherapy (SLIT) in elderly adults with either rhinitis or bronchial asthma. The aim of this study was to ascertain whether SLIT is effective in these patients. METHODS One hundred and sixty seven patients (aged 18-65 years) with persistent rhinitis and mild asthma, selected from 573 subjects allergic to house-dust mites, were treated with either standard chronic pharmacotherapy or SLIT plus drugs on demand. Monthly symptom/drug scores, respiratory function, methacholine (MCh) challenge and eosinophil count were scheduled at the beginning and end of the study. RESULTS We analysed two age groups (18-28 years, 49 patients) and 55-65 years, 40 patients). There were no differences between the groups at baseline but MCh sensitivity was lower in the older patients. At the end of treatment, SLIT achieved improvement in all variables (p< 0.001) in both age groups, but the global symptoms were lower in the younger patients (p=0.0002). There were also fewer new sensitizations in the SLIT groups (p=0.03) than in the "control"patients given standard pharmacotherapy, but with no relation to age. Asthma became worse only in the control groups, regardless of age. CONCLUSIONS SLIT reduces symptoms, drug consumption and the progression of the disease in both young and elderly subjects allergic to house-dust mites, with persistent rhinitis and mild bronchial asthma.