A relationship between allergic rhinitis and acute and chronic rhinosinusitis has been postulated for many years. Epidemiologic evidence suggests that such a relationship is likely. In addition, evidence of a common pathophysiologic mechanism linking these diseases is compelling and continues to evolve. Although a clear and definitive causal relationship remains to be elucidated, an increasing number of studies support the plausibility of this link. The current paradigm of the "unified airway" and evidence to support this model further strengthen this link. This article reviews the literature relating allergic rhinitis and acute and chronic rhinosinusitis.