An increased number of eosinophils and eosinophilic inflammation is associated with many diseases, from relatively common, specific to the respiratory tract, such as eosinophilic asthma or chronic rhinosinusitis with nasal polyps (CRSwNP), to rare multi-organ diseases, often with very high eosinophilia, such as eosinophilic granulomatosis with polyangiitis (EGPA) or hypereosinophilic syndrome (HES). Eosinophilic esophagitis (EoE) is also a disease that is difficult to diagnose and differentiate. Patients with multisystem diseases are at significant risk of disease progression and even mortality due to delayed diagnosis or inadequate treatment. In otorhinolaryngological practice, we most often observe increased eosinophilia in patients with a long-term history of difficult-to-control chronic rhinosinusitis with polyps, often with comorbid asthma or hypersensitivity to NSAIDs. Very often, the initial phase of EGPA, many years before the correct diagnosis is made, presents with chronic symptoms of inflammation in the upper and lower respiratory tract. Therefore, it is necessary to carefully analyze the symptoms and expand the diagnostics in patients with increased eosinophilia, although in some cases the differential diagnosis may remain difficult due to overlapping symptoms. It is worth noting that treatment options and response to therapy may vary among individual eosinophilic disorders. Many patients, especially those with HES and EGPA, require oral glucocorticoids for chronic therapy. Cytotoxic or immunomodulatory medications may be needed in cases with severe disease. New biological therapies, such as those targeting interleukin-5 or its receptor, or IL4/IL13 have shown great promise in inflammation control, exacerbations and relapses in patients with asthma, CRSwNP, HES, EGPA and EoE. Such therapies may reduce the side effects associated with long-term use of oral glucocorticosteroids or immunosuppressive drugs, and in patients with CRSwNP they may significantly reduce disease recurrences and the need for subsequent surgery, significantly improving the patients’ quality of life.