Allergen-specific immunotherapy is one of the cornerstones of allergic rhinoconjunctivitis treatment. Since the development of non-invasive administration forms with better safety profiles, there is an increasing tendency to prescribe immunotherapy in youngsters. However, no overview is available on the efficacy of immunotherapy in all its different administration forms in youngsters. Therefore, we systematically reviewed randomized controlled trials (RCTs) to evaluate the effect of immunotherapy with inhalant allergens on symptoms and medication use in children and adolescents with allergic rhinoconjunctivitis. Medline, EMBASE, the Cochrane Controlled Clinical Trials Register and reference lists of recent reviews and published trials were searched. RCTs including youngsters aged 0-18 yr with allergic rhinoconjunctivitis and comparing immunotherapy with placebo, symptomatic treatment or a different administration form of immunotherapy were included. Primary outcome measures were rhinoconjunctivitis symptom and/or medication scores. Methodological quality was assessed using the validated Delphi list. A method of best evidence synthesis, a rating system with levels of evidence based on the overall quality and the outcome of the trials, was used to assess efficacy. Six subcutaneous (SCIT), four nasal (LNIT), seven oral (OIT) and 11 sublingual (SLIT) immunotherapy trials, comprising 1619 youngsters, were included. Only 39% of the trials were of high methodological quality. For the SCIT and OIT subgroups the level of evidence for efficacy was conflicting. Moderate evidence of effect was found for LNIT. Analysis of the SLIT subgroup showed no evidence of effect. The evidence for the perennial and seasonal allergen trials within the subgroups varied from moderate evidence of effect to no evidence of effect. In conclusion, there is at present insufficient evidence that immunotherapy in any administration form has a positive effect on symptoms and/or medication use in children and adolescents with allergic rhinoconjunctivitis.