The case report is presented of a 47-year-old white woman with Cushing's disease treated by bilateral adrenalectomy in June 1981. A first computed tomography (CT) scan in September 1984 showed a voluminous pituitary adenoma with invasion of the sphenoid sinus and left parasellar extension. The tumour increased progressively in size, a suprasellar extension developed and the optic chiasm was eventually affected. In March 1988 and June 1989 the patient underwent two surgeries for the pituitary tumour, the second followed by radiotherapy. During this period, the ACTH values varied between 100 pmol/l and 403 pmol/l (normal: <13 pmol/l). After radiotherapy, a progressive shrinking of the tumour was observed and the ACTH concentrations decreased to a lowest value of 27.5 pmol/l. The patient was clinically well until September 1993 when, suddenly, the plasma ACTH concentration increased to very high levels (greater than 965 pmol/l). There was no evidence of tumour growth on the sellar CT scan. In January 1995, an ACTH-producing pituitary carcinoma was diagnosed, based on the presence of bone metastases. The patient died in May 1995.