Participants in study C-1073-400 (NCT00569582) will be invited to participate in this extension study to examine the long term safety of mifepristone in the treatment of the signs and symptoms of endogenous Cushing's syndrome. Total treatment duration may be up to 12 months or longer at the discretion of the Investigator.

Up to 50 subjects will receive mifepristone daily. Subjects completing 24 weeks of mifepristone treatment under Corcept protocol C1073-400 (NCT00569582) will be eligible to continue treatment for an additional 1 year. Assessments of safety, as evaluated by physical examinations, vital signs, laboratory tests and adverse events, will be made. Persistence of improvement in response to mifepristone treatment will also be evaluated during this extension study by assessing the continued or sustained improvement in the signs and symptoms of Cushing's syndrome.

Inclusion Criteria:

• Have completed the Week 24 visit and the 6-Week Follow-up visit of Corcept Study C-1073-400 (NCT00569582).
• In the opinion of the Investigator, are expected to maintain clinical benefit from mifepristone.
• Women of childbearing potential have a negative serum pregnancy test at Entry.
• Women of childbearing potential must be willing to use non-hormonal, medically acceptable methods of contraception during the study.
• Are able to provide written informed consent
• Are able to return to the investigative site to complete the study evaluations outlined in the protocol.
• Will not use systemic estrogens during the study.

Exclusion Criteria:

• Have an acute or unstable medical problem, which could be aggravated by mifepristone treatment.
• Are taking medications within 14 days of the Entry visit that a) have a large first pass metabolism that is largely mediated by CYP3A4 and which have a narrow therapeutic margin; and/or b) are strong CYP3A4 inhibitors.
• Female patients of reproductive potential, who are pregnant or who are unable or unwilling to use medically acceptable, non-hormonal methods of contraception during the study.
• Have received investigational treatment (drug, biological agent or device) other than CORLUX (mifepristone) within 30 days of Entry
• Have a history of an allergic reaction or intolerance to CORLUX (mifepristone)
• Have uncorrected hypokalemia (potassium level of <3.5 mEq/L) at Entry. Spironolactone or eplerenone is allowed to control hypokalemia.
• Postmenopausal women with a history of endometrial hyperplasia with atypia or pathological features consistent with endometrial carcinoma.
• Thickened endometrium on the Entry Visit transvaginal ultrasound that has not resolved after induction of menstrual bleeding with progesterone.
• Uncontrolled, clinically significant hypothyroidism or hyperthyroidism.
• Any woman with an intact uterus who has a hemorrhagic disorder or is being treated with an anticoagulant (e.g. warfarin, heparin).
• Have renal failure as defined by a serum creatinine of ≥2.2 mg/dL.
• Elevated total bilirubin >1.5 ULN, elevated ALT or AST ≥3X the upper limit of normal.