Aim: Different to inhibitory drugs of the renin-angiotensin-aldosterone system (RAAS), diuretics are known to decrease blood pressure (BP) and stimulate renin release by the kidneys. Despite plasma aldosterone (PA) level is mostly regulated by the RAAS activity, serum potassium has been shown to be an important factor in animal models and humans. Here we perform a systematic review and meta-analysis of randomized-controlled trials investigating the effects of diuretic therapy on PA and its correlation with change in potassium and BP. Methods: Three databases were searched: MEDLINE, EMBASE and The Cochrane Central Register of Controlled Trials (CENTRAL). Titles were firstly screened by title and abstract for relevancy before full-text articles were assessed for eligibility according to a pre-defined inclusion/exclusion criteria. Results: A total of 1139 articles were retrieved of which 45 met the pre-specified inclusion/exclusion criteria. The average standardised difference in mean PA change was similar for all classes of diuretic (mean, 95% CI); thiazide/thiazide-like 0.304 (0.169, 0.440), loop 0.927 (0.37, 1.49), MRA/potassium-sparing 0.264 (0.174, 0.355) and combination 0.466 (0.142, 0.789), Q = 6.475, P = 0.091. In subjects previously untreated with another antihypertensive, there was a significant relationship between PA change and change in systolic BP but no relationship with the change in potassium. Conclusion: In RCTs of diuretic therapy in hypertension, there is an increase in PA with all classes of diuretic and no between-class heterogeneity. Change in PA is not related with potassium but correlates to the change in BP in subjects previously untreated with another antihypertensive medication.