Diagnosis of chronic hypercortisolism still remains a challenge in many situations; we will insist on the diagnostic performance of midnight salivary cortisol:this approach combines two theoretical advantages for the diagnosis (measuring an index of circulating free cortisol, at the right time)，and offers a very convenient-and non traumatic-exploratory procedure for the patient. Salivary cortisol can be easily obtained, in outpatients, as repeated samples for long period of times, generating invaluable informations in patients with fluctuating hypercor-tisolism, and/or under treatment.