Ectopic adrenocorticotropic hormone (ACTH) syndrome (EAS) is a cause of Cushing's syndrome usually associated with neuroendocrine tumors. Olfactory neuroblastoma (ONB) is a rare malignant neoplasm of the olfactory epithelium. This is the case of a 56-year-old woman with an ONB presenting with EAS. After initiating metyrapone, she developed a Pneumocystis jirovecii pneumonia. Following successful treatment of the infection, she underwent surgical tumor excision and radiotherapy, which has been in remission for the past 3 years. The authors provide a literature review of the 30 previously published cases of ONB presenting with EAS. Most were reported in middle-aged men, with a recurrence rate of 15.6% (3 patients eventually died). A total of 9.5% of all reported had an infection after starting corticosteroid-blocking therapy. ONB is a very rare cause of EAS with poor prognosis and a relapsing course. In the presence of severe hypercortisolism, chemoprophylaxis for common opportunistic agents must be considered.