Primary aldosteronism (PA) is the cause of 510% of hypertension, surgically curable in patients with unilateral aldosterone-producing adenomas (APAs). However <1% of patients are currently diagnosed and cured. Newer and simpler modalities of diagnosis and treatment are required. The aim of FABULAS (a feasibility study of endoscopic ultrasound-guided ablation as a non-surgical, adrenal sparing treatment for aldosterone-producing adenomas) is to determine in 30 patients with left sided APAs if EUS-RFA is a safe alternative to adrenalectomy. Alpha and beta-blockade will be used to prevent catecholamine crisis during ablation. Safety outcomes include measures of adrenomedullary activation. Efficacy is evaluated by biochemistry, home and clinic BPs, and quantitative PET CT, using 11C-metomidate, at baseline and 6 months post ablation. 6 EUS-RFA procedures have been performed in 4 patients (mean age 67-years). The mean tumour size was 18 mm (range 936mm). Plasma metanephrine levels showed no increase during RFA. During the first 48 h of in-patient monitoring, 2 adverse events have been noted: AF in a patient with known paroxysmal AF, and an episode of pyrexia and raised CRP attributed to transient tissue infarction. All patients are between 4 and 16 months post-ablation with no further adverse events noted. There are several retrospective reports of successful percutaneous and retroperitoneal RFA ablation of APAs. FABULAS is the first prospective study, using a minimally invasive endoscopic route. After deliberately cautious, subtotal ablations in the first three patients, complete clinical and biochemical cure was achieved in the fourth. If we find EUS-RFA of left APAs to be safe and effective, this has the potential to revolutionise the future management of PA.