Background: Asthma is recognized as a major public health concern in the world. The aim of this investigation was to evaluate the prevalence of asthma by using the Global Allergy and Asthma Network of Excellence (GA 2 LEN) questionnaire and examine its association with chronic rhinosinusitis, in the province of Bushehr, Southwestern of Iran., Methods: In a cross-sectional, population-based study, a total of 5420 invited individuals, aged 15-65, were selected through a multi-stage, stratified, cluster random sampling and from which 5201 completed the GA 2 LEN questionnaire (response rate = 95.9%). The prevalence of asthma, current, and physician-diagnosed asthma were analyzed by using sex and age groups and the association of asthma and chronic rhinosinusitis (CRS) was investigated using a multiple logistic regression model., Results: Based on the information from the GA 2 LEN questionnaire, the overall prevalence of asthma in the population under study was 10.0% (95% CI 9.2-10.8). Moreover, the prevalence of current asthma was 8.9% (95% CI 8.1-9.7). Further, the prevalence of current early, late-onset and physician-diagnosed asthma within the asthma group was 51.1% (95% CI 46.5-55.7), 48.9% (95% CI 44.3-53.5) and 3.9% (95% CI 2.1-2.5), respectively. Additionally, CRS was more frequent among the participants with asthma [(57.3%, OR = 2.3; 95% CI 2.1-2.5)], and there was a significant association between CRS and current, early and late-onset of asthma (P < 0.001; OR = 4.4, 3.2 and 6, respectively)., Conclusion: This large population study conducted in the southwestern part of Iran suggests that the prevalence of asthma is high. Moreover, the result of this study showed a strong association of asthma with CRS; also after adjusting for sex, age, educational level, and smoking., Competing Interests: Competing interestsThe authors declare that they have no competing interests.