Background: Eosinophilia accompanies a large number of diseases and conditions, but information is lacking about the clinical characteristics of patients who are hospitalized due to this abnormality. Our aim was to determine the clinical profile and most informative diagnostic tests in patients hospitalized in a tertiary hospital because of hypereosinophilia. Methods: A retrospective review was done of the medical records of all patients hospitalized in a large urban medical center due to hypereosinophilia. All relevant clinical, laboratory, and imaging data were analyzed. Results: A total of 100 patients were included in the study (58 males and 42 females, mean age 55.2 ± 29 years). The blood eosinophil blood count was 4107 ± 7254/μl (mean ± SD) and this usually persisted for a few months. The cause of the eosinophilia was asthma or other atopic disease in 13% of the cases, allergic drug reaction in 6%, eosinophilic pneumonia in 10%, neoplastic diseases in 10%, idiopathic hypereosinophilic syndrome in 8%, Churg-Strauss Syndrome in 4%, infections in 10%, allergic fungal disease in 2%, and skin diseases in 3%; the cause remained unknown in 34% of cases. Conclusion: Guidelines are suggested for the investigation of patients with eosinophilia, including the level of the eosinophilia associated with specific diseases and the most informative diagnostic tests.