Cushing's syndrome in pregnant women is rare and difficult to be diagnosed because of the syndrome's association with oligomenorrhea or amenorrhea and the changes in cortisol metabolism during normal pregnancy. Cushing syndrome in pregnancy is usually confused with complicated pregnancy, such as preeclampsia or gestational diabetes, and its rarity leads to a low degree of clinical suspicion, often delaying diagnosis. We experienced a case of Cushing's syndrome in pregnancy, which had been considered as the severe preeclampsia and gestational diabetes due to uncontrolled hypertension and hyperglycemia. The pregnancy was terminated with an emergency cesarean operation at 30 weeks of gestation because of severe preeclampsia. In consequence of the evaluation about the Cushing's syndrome after delivery, the adrenal cortical adenoma of right adrenal gland was diagnosed and laparoscopic adrenalectomy was performed.