The widespread use of cross-sectional imaging leads to detection of adrenal tumours in up to 7–10% of ageing adults. The majority of these incidentalomas are benign adrenocortical adenomas, but the drivers causing most of these adenomas are not known. These lesions are now one of the most common referrals to endocrine centres causing significant workload.

Approximately 20% to 50% demonstrate biochemical evidence of cortisol excess in the absence of classical Cushing’s syndrome symptoms, a condition defined as mild autonomous cortisol secretion (MACS).

Large epidemiological studies demonstrate a continuum of increased risk of cardiovascular events, hypertension, type 2 diabetes, dyslipidaemia, central adiposity, osteoporosis, frailty, reduced quality of life, and excess mortality. Recent data question some of the clinical biochemical cut-points currently used for decision-making in clinical practice, whilst prospective surgical trials in the last couple of years have provided stronger causal links between MACS and adverse outcomes.

Nevertheless, key clinical challenges remain. These include the identification of the ideal surgical candidate for adrenalectomy, management of bilateral disease, and defining the role of medical therapies. These issues are brought into ever sharper focus as the recognised MACS population continues to expand, necessitating strategies to prevent both the overtreatment of low-risk individuals and the undertreatment of high-risk patients.