A 67-year-old patient with newly diagnosed acute myeloid leukemia developed acute respiratory failure with high-grade fever and bilateral pulmonary infiltrates. Blood cultures were sterile and no bacterial or fungal pathogen was identified in the endotracheal aspirate. The patient did not respond to antibiotic and antifungal therapy. One week after intensive care unit (ICU) admission, erythematous skin lesions appeared at the vascular catheter puncture sites. Sweet syndrome with pulmonary involvement was suspected and a treatment with corticosteroids was started. Sweet syndrome was confirmed by skin biopsy. After corticosteroid therapy respiratory symptoms rapidly improved, the patient became afebrile and the cutaneous lesions rapidly disappeared. Only three cases of Sweet syndrome presenting with pulmonary involvement before the appearance of skin lesions are reported in the literature. Even if typical skin lesions are initially absent, early recognition of Sweet syndrome with pulmonary involvement is important because of the possibility of severe respiratory impairment, which can be avoided through prompt administration of corticosteroids.