Adrenal adenoma is the commonest cause of Conn's syndrome. Sodium chloride infusion is a diagnostic test, aldosterone levels are suppressed in the normal population but not in Conn's syndrome patients.

Autoantibodies against 21-hydroxylase (P450c21) are common in Addison's disease. Granulomatous, lymphocytic inflammation of adrenal glands occurs in autoimmune adrenalitis. There is also a genetic predisposition in those with HLA-B8, HLA-DR3, HLA-DR4 haplotypes.