We describe the case of an 85-year-old man diagnosed with chronic myelomonocytic leukemia whose disease was treated with hydroxyurea for 3 months. He developed respiratory symptoms that were extensively investigated. Despite the intensive treatment, he died of respiratory failure eleven days later. An autopsy revealed diffuse interstitial inflammation of both lungs consistent with drug-induced inflammation. A drug lymphocyte stimulation test was positive for hydroxyurea. Taken together these findings demonstrated that severe interstitial pneumonitis was induced by this drug. Physicians using hydroxyurea must be aware of its potentially life-threatening pulmonary toxicity.