BACKGROUND: The symptoms of allergic rhinitis may be worsened by a viral respiratory infection. However, there are few data on the presence of respiratory virus in patients with allergic rhinitis. OBJECTIVE: To evaluate whether patients with allergic rhinitis have an increased frequency of respiratory virus detection in a prospective case-control study. METHODS: Fifty-eight adult patients diagnosed with perennial allergic rhinitis were evaluated from September 2011 through June 2012. A control group of 61 adult patients without allergy was included. Multiplex polymerase chain reaction was used to detect respiratory viruses in nasal lavage samples. RESULTS: Respiratory viruses were detected in 25 of 58 patients (43.1%) with perennial allergic rhinitis, but in only 15 of 61 control patients (24.6%). In virus-positive samples, multiple viruses were detected in 9 of 25 patients (36.0%) with perennial allergic rhinitis but in only 2 of 15 control patients (12.5%). Rhinovirus was the most common virus in patients without allergy and those with allergic rhinitis. There were significant differences in the detection rates of overall and multiple respiratory viruses and rhinovirus between the 2 groups (P < .05). However, in patients with allergic rhinitis, there was no statistically significant association between the detection of respiratory viruses and symptom scores. CONCLUSION: This study shows that there is a high prevalence of respiratory viruses, especially rhinovirus, in patients with allergic rhinitis. Subsequent studies are needed to determine the clinical significance of highly prevalent respiratory viruses in patients with allergic rhinitis.