Allergic rhinitis (AR) and asthma coexist frequently and a dual treatment is recommended by prescribing topical nasal plus oral inhaled corticosteroids. The purpose of this study was to assess the efficacy of a nasally inhaled corticosteroid aiming at concomitant control of AR and asthma. A controlled trial was conducted among 60 patients with AR and asthma, aged 6–18 years, who were randomized into two groups. During 8 weeks, the experimental group (30 patients) received exclusively fluticasone propionate hydrofluoroalkane (FP-HFA) inhaled through the nose (mouth closed) using a large volume spacer attached to a face mask. The comparison group (30 patients) received a nasal spray of isotonic saline plus oral inhalation of FP-HFA through a mouthpiece attached to the same spacer. Clinical scores for AR and asthma, nasal inspiratory peak flow (NIPF), and spirometry were assessed by blinded observers. There was a significant improvement in AR scores and NIPF in the experimental group (P ≤ 0.01) up to week 8, when a worsening was observed after the intervention was interrupted. Asthma symptoms score, forced expiratory volume (FEV)1, and FEF25−75% were not statistically different between groups at the baseline visit or along follow-up visits (P ≥ 0.20). Prebronchodilator FEV1 (% predicted value) improved by 10% in both groups, comparing values at inclusion with those obtained at the end of follow up. Our results suggest that nasally inhaled FP-HFA through a spacer may control AR and asthma in children and adolescents. This approach is likely to result in higher compliance, lower costs, and fewer side effects.