SummaryOBJECTIVEAdrenal insufficiency (Al) is a well known complication of AIDS. However, the clinical and biochemical features of Al in HIV infected patients have not been extensively studied.DESIGNA restrospective clinical study.PATIENTSWe reviewed clinical records of 74 AIDS patients with clinical and/or biochemical indications of Al who underwent Synacthen testing in order to determine adrenocortical function during a 5‐year period.MEASUREMENTSAI was diagnosed when Cortisol levels failed to rise above 496 nmol/l at any time during the test. Cortisol was measured by RIA.RESULTSSixteen patients (22%) were diagnosed with Al. Most were young males and all of them had a known risk factor, principally I.v. drug users. The main complaint was fatigue. Hyponatraemia or hyperkalaemia were uncommon. All of them were severely immuno‐suppressed, with AIDS‐defining conditions from at least 6 months before the diagnosis of Al, and had been diagnosed with at least one disease that has been reported to produce Al in AIDS patients. Survival was poor. Thirteen of these patients (81%) died within 6 months. Basal cortisol levels were lower than 275 nmol/l in 75% of patients with Al but in only 2% of the group of 58 patients who had normal adrenal responses to Synacthen.CONCLUSIONSAdrenal insufficiency features in AIDS patients with advanced disease, without specific findings and with a history of previous opportunistic diseases. Basal cortisol values at 0830 h lower than 275 nmol/l are highly suggestive of adrenal insufficiency in patients with