Although no hypothesis is universally accepted, allergic rhinitis (AR) may play an important role in the occurrence of rhinosinusitis. This study was carried out to investigate the frequency and severity of rhinosinusitis among patients with seasonal or perennial AR. This study included 73 patients with AR. Findings related to rhinosinusitis of these patients were demonstrated by computed tomography (CT), and were scored according to the Lund-Mackay CT scan staging system. Fifty-two of the 73 patients (71.2%) were shown to have findings of rhinosinusitis. Of these 52, twenty-four patients (77.4%) had perennial AR and 28 (66.7%) patients had seasonal AR. The mean total CT staging score of rhinosinusitis was 4.2 +/- 3.2 in patients with perennial AR and 2.6 +/- 1.3 in patients with seasonal AR. Although the frequency of rhinosinusitis among patients with perennial AR was higher than among seasonal ones, this was statistically insignificant (p = 0.32). But CT staging scores of rhinosinusitis among the patients with perennial AR were significantly higher than among the seasonal AR group (p = 0.014). Although there was no significant difference between the frequency of rhinosinusitis of seasonal and perennial AR, the severity of rhinosinusitis was more severe in cases with perennial AR, in this study. Early management of an allergic disease is essential if its long-term consequences are to be prevented or minimized.