The prevalence and severity of rhinitis and/or chronic rhinosinusitis (CRS) related to asthma severity was the aim of this study in a cohort of asthmatic patients. METHODS. Asthmatic (N=492), mean age 45(15) yr, female 70.5%, according to GINA: (intermittent 17.3%; persistent 82.7% [mild 24.6%, moderate 31.4%, severe 26.7%]) in a prospective study carried out in 2010-2011 by pneumonologists and ENT specialists of 23 centres. Allergic (AR) and non-allergic (NAR) rhinitis and CRS with (CRSwNP) and without (CRSsNP) nasal polyps were evaluated according to ARIA and EPOS by symptoms, prick test, endoscopy, and sinus CT scan. Asthma control according to GINA and Asthma Control Test (ACT). RESULTS. No sinonasal disease 14.2%, rhinitis 49.6% (AR: 37.0%; NAR: 12.6%), and CRS 36.2% (CRSsNP: 16.7%; CRSwNP: 19.5%;). Most AR (78%) and NAR (84%) comorbidities were present in intermittent and mild to moderate persistent asthmatics. CRSsNP was similarly frequent in all asthma severity levels while CRSwNP was associated to severe asthma (48%, P CONCLUSIONS. 1 st ) Most patients (85.8%) have concomitant rhinitis or chronic rhinosinusitis; 2 nd ) Intermittent and mild to moderate asthma are associated with rhinitis, either allergic or non-allergic; 3 rd ) Severe asthma is associated with CRS with nasal polyps, specially in non-atopic patients; and 4 th ) Both asthma severity and sinus ocupancy are associated with a poorer asthma control in nasal polyposis.