In this study, we evaluated the relationship between rhinosinusitis to the severity of asthma in asthmatic patients.This cross-sectional study was conducted on 90 patients with asthma referring to Imam Khomeini Hospital in Ardabil city. Asthma control stepping method was used for staging of asthma severity. Patients' clinical signs and paraclinical findings were individually evaluated and compared with particular attention to the presence or absence of rhinosinusitis. Chi square and t-test were used to analyze the data in SPSS15 software.Rhinosinusitis was found in 66 (73%) of the 90 patients. The Forced Expiratory Volume in 1 second (FEV1) was significantly lower in the patients who also had rhinosinusitis (P=0.002).Comparing severity of asthma, most of the patients with rhinosinusitis were in stage3 (42.4%) but most of the patients without rhinosinusitis were in stage1 (41.6%) (p=0.002).The results of this study confirm the correlation between asthma severity and rhinosinusitis in asthmatic patients. Therefore, in diagnosing asthma in patients, the possibility of the rhinosinusitis should be determined and treated.