This phase III study is an open-label extension study to be conducted at approximately 21 investigational sites across 3 countries. The study will evaluate the long-term safety and tolerability of Chronocort in participants aged 16 years and over when used as treatment for Congenital Adrenal Hyperplasia (CAH).

Participants in eligible countries completing one of the specified previous Chronocort studies (DIUR-006 and DIUR 014) can either continue Chronocort treatment (if the participant received Chronocort in the feeder study) or switch to Chronocort treatment (if the participant received standard glucocorticoid therapy in the feeder study) in this open-label extension study. All participants choosing to enter this extension study will have the study procedures fully explained and informed consent obtained, prior to, or at the last visit of the feeder study. Participants who agree to take part in this extension study will then undergo the final visit of the feeder study, with the assessments conducted at the final visit also providing the baseline data for this DIUR-015 extension study where relevant (note participants who are withdrawn from treatment due to titration issues in study DIUR-014 are eligible to enter at the discretion of the Investigator, as long as all DIUR-014 safety assessments and the end of study visit are completed). Once all the baseline assessments are completed, participants will be given sufficient Chronocort to use until the next visit (the study pharmacies will be supplied with Chronocort for dispensing to participants according to the Investigators' instructions).

Outcome measures in this study will be assessed versus either the 'initial study baseline' (measurements taken at the start of participation in an interventional Chronocort study, regardless of the treatment assignment in this feeder study) or the protocol-defined 'pre-Chronocort baseline' (measurements taken prior to the first dose of continuous Chronocort) or the 'DIUR-015 baseline' (measurements taken at the start of participation in DIUR-015 study).

Inclusion Criteria:

• Participants with Congenital Adrenal Hyperplasia (CAH) who have successfully completed Chronocort study DIUR-006 (sites in France and US only) or study DIUR-014.
• Participants who are capable of giving signed informed consent/assent, which includes compliance with the requirements and restrictions listed in the study's informed consent form (ICF) and in the protocol.

Exclusion Criteria:

• Participants with clinical or biochemical evidence of hepatic or renal disease e.g., creatinine >2 times the upper limit of normal (ULN) or elevated liver function tests (alanine aminotransferase [ALT] or aspartate aminotransferase [AST] >2 times the ULN).
• Participants with a history of malignancy (other than basal cell carcinoma successfully treated >26 weeks prior to entry into the study).
• Participants with a history of bilateral adrenalectomy.
• Participants with any other significant medical or psychiatric conditions that in the opinion of the Investigator would preclude participation in the study.
• Participants with a co-morbid condition requiring daily administration of a medication or consumption of any material that interferes with the metabolism of glucocorticoids.
• Participants on regular daily inhaled, topical, nasal, or oral steroids for any indication other than CAH.
• Participants anticipating regular prophylactic use of additional steroids e.g., for strenuous exercise.
• Participation in another clinical study of an investigational or licensed drug or device within 3 months prior to inclusion in this study, except for another clinical study with the current formulation of Chronocort.
• Females who are pregnant or lactating.
• Participants, who in the opinion of the Investigator, will be unable to comply with the requirements of the protocol.
• Participants who routinely work night shifts and so do not sleep during the usual night-time hours.
• Participants with a body weight of 50 kg or less (Note: this exclusion criterion is only applicable for French sites).