Objective: The prevalence and costs of allergic rhinitis (AR) in the U.S. are estimated to be very high. Recently, research has reported that not all AR symptoms are of equal importance to patients. In particular, evidence is mounting that nasal congestion is the most bothersome symptom of AR and thus may account for most of the burden of illness. However, unlike AR which has an ICD-9-CM code thus facilitating estimates of burden of illness, the cost of nasal congestion must be obtained indirectly. The purpose of the present analysis is to estimate the national costs of AR that are attributable to nasal congestion. Methods: Data come from a recent national study of the effect of AR symptoms on patients' lives (e.g., sleep, daytime somnolence, mood, and work and school productivity). These relative effects of nasal congestion were then applied to U.S. cost estimates derived from the literature and a national employer claims database to estimate some of the economic burden of AR that could be attributed to nasal congestion. Results: Results suggest that almost three-fourths of the cost associated with burden of illness related to AR is attributable to nasal congestion. Thus, approximately $3.4 billion of the $4.8 billion in direct costs for AR and approximately $3.1 billion of the $4.3 billion in indirect costs for AR can be attributed to nasal congestion. Conclusion: The direct and indirect costs attributable to nasal congestion are substantial. These high costs emphasize the importance of diagnosing and treating nasal congestion.