Background Primary aldosteronism can be treated medically but there is no standardised method to evaluate treatment outcomes. We aimed to develop criteria for assessing the outcomes of targeted medical treatment of primary aldosteronism, analyse outcomes across an international cohort, and identify factors associated with a complete treatment response. Methods An international panel of 31 primary aldosteronism experts used the Delphi method to reach consensus on the definition of complete, partial, or absent biochemical and clinical outcomes of medical treatment of primary aldosteronism. Clinical data at baseline and 6-12 months post-treatment were collected from patients with primary aldosteronism who started targeted medical treatment between 2016 and 2021 at 28 participating centres. Findings Consensus was reached for defining complete, partial, or absent biochemical or clinical response. Of 1258 patients (with a mean age of 52 years [SD 11<middle dot>5] and of whom 610 [48<middle dot>5%] were female and 648 [51<middle dot>5%] were male), 1057 (84<middle dot>0%) had biochemical outcome data (559 [52<middle dot>9%] had a complete biochemical response). The median daily dose of spironolactone was significantly higher for those with a complete biochemical response than for those without (40 mg [IQR 25-50] vs 25 mg [20-50]; p=0<middle dot>011). Of the 1248 patients with clinical outcome data, 228 [18<middle dot>3%] had a complete clinical response whereas 227 (18<middle dot>2%) had an absent response. Patients with a complete clinical response were more likely than those with partial or absent clinical response to be women (OR 2<middle dot>099, 95% CI 1<middle dot>485-2<middle dot>968; p<0<middle dot>001), require lower doses of antihypertensive drugs at baseline (0<middle dot>687, 0<middle dot>603-0<middle dot>782; p<0<middle dot>001), and were less likely to have microalbuminuria or left ventricular hypertrophy (0<middle dot>584, 0<middle dot>391-0<middle dot>873; p=0<middle dot>009). Interpretation The Primary Aldosteronism Medical Treatment Outcome (PAMO) criteria represent an internationally developed outcome standard that can guide clinical practice and research into primary aldosteronism. Efforts to optimise treatment intensity and minimise factors associated with an absent treatment response are needed to improve patient outcomes. Copyright (c) 2025 Elsevier Ltd. All rights reserved, including those for text and data mining, AI training, and similar technologies.