Corticosteroid hypersensitivity is a rare, but troublesome condition often mimicking the symptoms of the underlying disease and therefore probably underdiagnosed. Our objective is to underline the importance of increased awareness of corticosteroid hypersensitivity and of determining the tolerability to other corticosteroid preparations and thus identify a safe treatment alternative. We report a case of corticosteroid hypersensitivity in a 65-year-old woman with a history of difficult-to-treat asthma and systemic corticosteroid allergy admitted with increasing dyspnea and dry cough. The patient was diagnosed with hypereosinophilia, apical fibrosis, and basal pulmonary infiltrations. A prick test and a prolonged challenge test were performed to find a suitable corticosteroid to treat her hypereosinophilia. In conclusion, it is compulsory to perform cutaneous prick and intradermal test, but many cases will only be diagnosed correctly by intravenous or oral challenge test.