Compare the time of clinical improvement and adherence to treatment among the group receiving vitamin D against the group receiving placebo Analyze the relationship between vitamin D values, total serum IgE, serum eosinophil and nasal cytology in both groups before and after treatment Assess the safety of vitamin D by serum calcium. TH17 and Treg quantify cells before and after treatment. MATERIAL AND METHODS This is a interventional, prospective clinical trial randomized placebo-controlled, double-blind study including paediatric patients (children 3-12 yr old) with allergic rhinitis, with parallel group: Immunotherapy + Placebo and Immunotherapy + Vitamin D. Patients prior informed consent include more patients being female and male of 3 to 12 years old. They will be randomized and in the same proportion. The sample was calculated using the G Power program to achieve an effect size of 0.65, with alpha = 0.05, statistical power = 80% and 20% losses to mean difference of 2 independent groups, the result was 80 patients, 40 per group. Monitoring will be conducted at 0, 3 and 6 months, assessing clinical and laboratory parameters with the questionnaire RQLQ, TNSS, CARACT KIDS, ARIA, GINA.