Introduction: Chronic rhinosinusitis (CRS) is a multifactorial disease. Allergies are considered a predisposing factor to CRS; however, this remains controversial. The objective of this research was to investigate the prevalence of co-morbidities and allergic reaction, and to specify the most common allergens in patients with confirmed CRS.   Materials and Methods: One hundred patients with signs and symptoms of CRS who met the diagnostic endoscopic and radiologic criteria of chronic rhinosinusitis were selected. They filled out a questionnaire and underwent a skin prick test for the common inhalant allergens. Allergic rhinitis was diagnosed according to the history and positive skin prick tests.   Results: The mean age of patients was 34. Males were slightly more involved (54%). The prevalence of polypoid and none-polypoid rhinosinusitis was 54% and 46% respectively. The patients’ most common symptoms were nasal discharge (95%), blockage (94%), smell disorders (63%), cough (45%), halitosis (41%), lethargy (37%), and aural fullness (36%). Allergy to at least one allergen was noted in 64% of the CRS patients which is higher than general population in Mashhad, Iran with allergic rhinitis (22.4%). Salsola was the most common allergen. There was no significant difference in allergic reactions between polypoid and non-polypoid CRS patients.   Conclusion:  Allergic reactions was found in Iranian CRS patients with or without polyposis to be much higher than general population in Mashhad with allergic rhinitis alone.