Eosinophilic chronic rhinosinusitis is an adult-onset refractory rhinosinusitis, often associated with adult-onset asthma and aspirin intolerance. Patients often present with olfactory disturbances and nasal obstruction, which significantly reduce their quality of life. Eosinophilic granulomatosis with polyangiitis (EGPA) is a type of antineutrophil cytoplasmic antibody-associated vasculitis, characterized by eosinophilia, severe asthma, and systemic vasculitis. EGPA is a systemic disease that involves both ischemic damage to multiple organs and eosinophilic organ damage. Eosinophilic chronic rhinosinusitis and EGPA share a common pathogenesis of eosinophilic inflammation in the airways, and it is sometimes difficult to differentiate between the two diseases, especially in patients who have no obvious evidence of organ damage other than significant rhinosinusitis with eosinophilic inflammation. However, given their differing prognoses, it is important for otorhinolaryngologists to promptly recognize and diagnose these conditions, especially when EGPA is suspected. When treating eosinophilic chronic rhinosinusitis, it is necessary to consider the potential for EGPA and to evaluate the entire body, including comorbidities, to ensure appropriate treatment. This article highlights the key characteristics of both diseases, emphasizing the need forotorhinolaryngologists to be well-informed about EGPA for effective diagnosis and management.