The patient was a 26-year-old man with Cushing's disease who underwent transsphenoidal microscopic surgery for a pituitary microadenoma. His postoperative course was uneventful, but he died suddenly five years after the operation. At autopsy, a ruptured dissecting aneurysm with marked atherosclerosis was observed in the aorta. In the pituitary, a small focus of adrenocorticotropic hormone (ACTH) producing adenoma, possibly residual adenoma, was detected and Crooke's degeneration was observed in the non-tumorous pituitary gland. But immunohistochemical patterns of pituitary hormones in the non-tumorous pituitary gland were normal and the adrenal cortex was unremarkable. In the hypothalamus, corticotropin-releasing hormone immunoreactivity was not detected and arginine vasopressin was sporadically positive. Considering these findings, this patient may have developed subclinical hypercortisolism due to the residual adenoma at the time of autopsy, despite clinical remission. Cushing's syndrome is considered to be a risk factor dissecting aneurysm, and in this case the metabolic changes in Cushing's disease may have influenced the development of the dissecting aneurysm. Periodic cardiovascular re-evaluations should therefore be performed when there is clinical remission of Cushing's syndrome.