Abstract Nocardia is an uncommon, opportunistic infecting organism. The radiographic appearance of pulmonary nocardiosis is most commonly cavitary or lobar infiltration. Particular attention is focused upon the acute necrotizing course of nocardiosis as experienced in 5 patients. Difficulty with laboratory diagnosis, the frequent use of steroid therapy, and the necessity of sulfonamide therapy require that clinicians and radiologists be aware of the disease process, especially in the clinical setting of malignant tumors and long-term adrenocorticosteroid therapy.