Background: Previous studies have suggested that single-allergen-specific immunotherapy (SIT) may prevent sensitization to other airborne allergens in monosensitized children. We aimed to assess the prevention of new sensitizations in monosensitized children treated with single-allergen SIT injections in comparison with monosensitized patients given appropriate pharmacologic treatment for their disease. Methods: A total of 147 children with rhinitis and/or asthma monosensitized to house dust mite were studied; 45 patients underwent SIT with adsorbed extracts and 40 patients underwent SIT with aqueous extracts for 5 years. The control group was comprised of 62 patients given only pharmacologic treatment for at least 5 years. Skin prick tests, medication scores for rhinitis and asthma, and atopy scores according to skin prick tests were evaluated at the beginning and after 5 years of treatment. Results: All groups were comparable in terms of age, sex, and disease characteristics. At the end of 5 years, 64 out of 85 (75.3%) in the SIT group showed no new sensitization, compared to 29 out of 62 children (46.7%) in the control group (P=.002). There were no differences between the SIT subgroups with regard to onset of new sensitization (P=.605). The patients developing new sensitizations had higher atopy scores (P=.002) and medication scores for both rhinitis (P=.008) and asthma (P=.0 13) in comparison to patients not developing new sensitizations after 5 years of SIT Conclusion: According to our data, SIT has the potential to prevent the onset of new sensitizations in children with rhinitis and/or asthma monosensitized to house dust mite.