A 25-year-old primigravid woman presented with Cushing's syndrome at 23 weeks gestation; serum cortisol was 1090 nmol/l at 0900 h, 1230 nmol/l at 2200 h; basal urinary free cortisol excretion was 3680 nmol/24 h, and 8830 nmol/24 h after dexamethasone 8 mg daily for 48 hours; plasma ACTH was < 1.1 pmol/l. CT scan of the adrenal glands showed bilateral adrenal hyperplasia. The hypercortisolism was controlled with metyrapone until elective delivery of the fetus by Caesarean section at 34 weeks gestation because of a decline in growth. No adverse fetal effects of metyrapone treatment were apparent, maternal outcome was uncomplicated and wound healing was unimpaired. Maternal adrenocortical function had returned to normal within 4 weeks of the cessation of pregnancy and biochemical remission has been maintained up to 9 months post-partum. Metyrapone therapy is effective in controlling the hypercortisolism in certain cases of Cushing's syndrome complicating pregnancy.