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English⧼Colon⧽ F2: Case 2 – 11C-metomidate PET-CT identifies unilateral primary aldosteronism despite mineralocorticoid receptor antagonist therapy. A 63-year-old man with a 10-year history of primary aldosteronism treated medically with mineralocorticoid receptor antagonist therapy was referred for reassessment and consideration of possible adrenalectomy. His blood pressure had previously proved difficult to control until the introduction of spironolactone, and the patient was reluctant to discontinue this to permit adrenal vein sampling (AVS). MRI demonstrated an 11 mm right adrenal nodule (a). 11C-metomidate PET-CT confirmed avid tracer uptake within this lesion [target:background standardized uptake value (SUV)max ratio 2.45] (b). He underwent laparoscopic right adrenalectomy, with histology confirming an adrenal cortical adenoma. Postoperatively, he had complete resolution of his biochemical hyperaldosteronism and hypertension with no requirement for antihypertensive therapy. This case illustrates the utility of 11C-metomidate PET-CT in establishing unilateral primary aldosteronism even in patients who are unable or unwilling to discontinue mineralocorticoid receptor antagonist therapy.