Specific immunotherapy (SIT) is one of the treatment modalities recomended for the management of asthma and allergic rhinitis by international guidelines. A potential benefit of immunotherapy (IT) is to prevent the development of sensitisation to new allergens. There is stil no conclusion on this subject. One hundred twenty-twochildren 8-18 years old with intermittent asthma, with or without allergic rhinitis, all of whom were monosensitised to house dust mite (HDM) were selected. Sixty two of these children accepted to receive SIT with HDM extract for 4 years and the remaining 60 did not accept SIT and were treated with asthma medications only. This second group of children served as the control group. At the end of the 4-year study period, 36 of the 53 patients (67.9%) in the SIT group showed no new sensitizations, compared to 38 of 52 (73.0%) in the control group (p = 0.141). The most frequent new sensitizations at the end of the study were pollens, grasses and olive polen, followed by animal dander, alternaria and cockroach. In conclusion, SIT may not prevent the onset of new sensitizations in asthmatic children monosensitized to house dust mites. Further investigation is required to clarify the immunologic mechanisms and other factors by which SIT reduces or not the development of new sensitizations in monosensitized children.