Disease of the nose and paranasal sinuses is almost present. In all patients with cystic fibrosis, the complaints are usually not reported by patients, due to the fact that these symptoms are usually present at birth and children are adapted to them. Many of the previous studies referred to nasal congestion as the most common symptom of the disease. In the present study, the most common complaint in children was nasal congestion (61.7%). In addition, there was no relationship between symptoms and age, sex, height, and weight that was consistent with the most recent studies (
9,
17,
18). In our study, 31.9% of nasal polyps were diagnosed using rigid endoscope examination. In previous studies, this diagnosis rate has been reported to be very variable. In a literature review by Carvalho and colleagues, the incidence of polyposis in patients with cystic fibrosis varied from 6% to 67% (
17) . In another study, 44% of patients had nasal polyps (
19). It should be noted that these studies employed different methods for diagnosing polyps. Some of them just used anterior rhinoscopy, while most studies used an endoscopy with different methods. In most studies, similar to our study, rigid endoscope was used in outpatients (
20,
21). In a study, rigid endoscope was done in the operating room under general anesthesia, while Freitas and colleagues used flexible endoscopy in outpatients (
20,
21).
By reviewing previous studies, the diagnosis of rhino sinusitis and nasal polyps in patients with cystic fibrosis was different (history, CT scan, and nasal endoscopy). Almost all patients have some degree of radiological changes and evidence of disease of the nasal mucosa and sinuses. Various studies have offered different figures of these findings. However, the over diagnosis of nasal polyposis, based on radiological findings, has been common in most studies (
11,
22). In our study, the most common sinus with opacification was the maxillary sinus with 5.74% involvement, followed by ethmoid involvement (54.2%). This was consistent with most previous findings. In a study on 34 patients with cystic fibrosis at the age of six, Boari and co-workers evaluated the results of the questionnaires, nasal endoscopy, and Sino nasal CT scans in the diagnosis of chronic rhino sinusitis. According to this study, the most commonly involved sinuses were the maxillary sinus (91.9%) and the anterior ethmoid (83.9%). According to this study, the three different methods had different diagnosis power for detecting rhino sinusitis. This diagnosis power was more in CT scan and less in questionnaire-based reviews (
23). In our study, the least amount of involvement was observed in the frontal sinus, which is justified considering that the present study was conducted on the pediatric population and considering the evolution of the frontal sinus at older ages. We also found some degrees of hypoplasia in at least one of the sinuses (51.5%) and the frontal sinus accounted for the highest percentage (48.9%). Frontal sinus agenesis is one of the notable features among patients with cystic fibrosis and chronic rhino sinusitis (
9,
22,
24) . In this study, there was no statistical relationship between the presence of polyps with the examination, age, and symptoms, as well as examination findings, such as rhinorrhea, and sinonasal CT findings. Accordingly, it can be stated that the patients’ history, CT scans, and physical examinations (rhinorrhea in anterior rhinoscopy) did not allow accurate diagnosis of chronic rhinosinusitis with nasal polyps in children with cystic fibrosis and nasal endoscopy is the most reliable method for the diagnosis of nasal polyps.