Objective Sinusitis is a common complaint in children with cystic fibrosis. However, the actual prevalence of chronic rhinosinusitis and its effect on the quality of life of children have not been well considered. Therefore, the objective of this study was to determine the effect of sinonasal quality of life in children with cystic fibrosis. Materials and methods This study was a diagnostic study performed on 80 children with cystic fibrosis ranging from 2 to 20 years old, who were referred to the cystic fibrosis clinic of Masih Daneshvari Hospital from 2017-2018. The questionnaires used in this study were chronic rhinosinusitis screening questionnaire based on the European task force and the evaluation of the sinonasal quality of life was based on the SN-5 survey. Results Of the 80 patients with fibrosis from 2 to 20 years old who were recruited in the study, 41 patients were female (51.3%) and 39 were male (48.8%). In 61 cases (76.3%), there was no chronic rhinosinusitis and 19 cases (23.8%) had chronic rhinosinusitis. The mean SN-5 score in 19 patients with chronic rhinosinusitis was 3.4105 and the mean score of patients without rhinosinusitis was 1.8426, with a P-value of 0.000. The mean SN-5 score was significant between the two groups. In patients with nasal congestion, there was a significant difference in quality of life factors such as sinus infection, nasal obstruction, and allergy symptoms (P<0.001). In patients with facial pain, there was a significant difference in quality of life factors such as sinus infection, nasal obstruction, allergic symptoms, and physical activity limitation (P <0.001). There was also a significant difference in the quality of life factors such as sinus infection, nasal obstruction, and allergy symptoms in patients with postnasal drip (P <0.001). Conclusion In children with cystic fibrosis, the quality of life of sinonasal has a significant relationship with absence of chronic rhinosinusitis. This study showed that children with chronic renosinusitis have significantly lower quality of sinonasal life than children with chronic rhinosinusitis. The results demonstrated that quality of life scores in sinus infections, nasal obstruction, and allergy symptoms were significantly higher in patients with chronic rhinosinusitis than in those without chronic rhinosinusitis. The findings of this study are important for improving children's health related quality of life, as it leads to promoting communication between the patient and the health care provider, identifying overlooked problems, monitoring the progress of the disease and the burden of treatment, and promoting interventions in the daily life of patients.