Expression of proteins involved in steroidogenesis, namely steroidogenic acute regulatory protein (StAR), 11β-hydroxylase (CYP11B1), aldosterone synthase (CYP11B2) and 17α-hydroxylase (CYP17A1), were analyzed by immunohistochemistry in ACC (n = 14), adenomas presenting with Cushing’s syndrome (ACAc) (n = 11) and clinically non-functioning adenomas (ACAn) (n = 15). The gene discussed is CYP17A1; the disease is Cushing syndrome due to macronodular adrenal hyperplasia.