A 52-year-old woman developed recurrent hypercortisolism 3 yr after successful surgical treatment of Cushing's disease. At postmortem, eosinophilic pituitary tissue showing positive ACTH immunohistochemical staining was present in the frontal lobe and cerebellum but there was no tumor in the sella. In the absence of a pituitary tumor, extrasellar ACTH producing tissue could arise from seeding of the cerebrospinal fluid with tumor cells at the time of operation or from an atypical pituitary carcinoma. In this report we review the mechanisms of intracranial dissemination of pituitary tissue and ACTH-secreting pituitary carcinomas, including parasellar invasion, meningeal seeding, and cerebrospinal and hematogenous spread.