Rationale, aims and objective: Eosinophilia is rare, but one of the important reasons to refer patients to pneumonological centers. Determining its etiology has practical implications for therapeutic intervention and disease prognosis. The study aimed to determine the role of peripheral eosinophilia in the diagnosis of lung disorders. Methods: The prospective study included 46 consecutive patients diagnosed with peripheral eosinophilia with coexisting respiratory symptoms and/or radiologically detected lung lesions. All patients underwent standard diagnostic procedures, including a detailed clinical history review, physical examination, routine laboratory tests with basal cardiological examinations, and serological tests to detect parasites and allergies. Other procedures carried out depended on the symptoms of each patient. Results: Severe eosinophilia (≥5,000 cells/μL) was associated with extrapulmonary involvement and constitutional symptoms. Skin, heart, and pleural diseases were more frequent in these patients than in patients with mild or moderate eosinophilia (p=0.010, p=0.040, and p=0.007, respectively), and only these patients showed signs of kidney disease (p=0.006). Vasculitis was significantly more frequent in the severe eosinophilia group (p=0.048) than in the other two groups. In patients with moderate eosinophilia (1,500-5,000 cells/μL), extrapulmonary symptoms were less common, although signs of cardiac involvement were confirmed in 44% of subjects. In this group, vasculitis was the most commonly observed disease (42% of cases). Mild eosinophilia (<1,500 cells/μL) was mainly associated with airway disease. In this group, vasculitis and interstitial lung diseases were identified, but most were not typically connected with eosinophilia. Conclusion: Identification of peripheral eosinophilia essentially determines diagnostic procedures in patients with lung disorders and can be a useful indicator of disease etiology.