Background:Kwashiorkor is an edimatous form of severe malnutrition and is the predominant form of childhood malnutrition in Malawi. Potassium depletion is common and contributes to the high mortality. The aim of this study was to determine if high potassium supplementation improves the outcome of kwashiorkor treatment.Methods:We performed a randomised, double-blind, placebo-controlled, clinical trial of high potassium supplementation in 99 children with kwashiorkor. Controls (n = 51) received a standard potassium intake of 4.7 mmol/kg/day. The intervention group (n = 48) received 7.7 mmol/kg/day. All cases (intervention and control groups) were treated in the hospital-based Nutrition Rehabilitation Center and received a standard treatment regime of mild feeds, mineral and vitamin supplements, and antibiotics.Results:There was no significant difference in length of hospitalization, or time for resolution of oedema between groups. The case-fatality rate was reduced by 33% in the high potassium intervention group (13/48) compared to controls (21/51). There was a significant reduction in late deaths (13 in controls vs 3 in intervention group; odds ratio 5.3, 95% confidence interval 1.2-31.0) but no difference in early deaths (0-5 days). The intervention group also had significantly fewer presumed septic episodes (3 vs 18, odds ratio 8.9, confidence interval 2.2-50.9), respiratory symptoms, and new skin ulcerations than controls.Conclusions:The high potassium supplementation reduced mortality and significant morbidity in kwashiorkor. This may be due to improved myocardial and immune function from earlier repletion of intracellular potassium. We recommend that the standard potassium supplement for the initial phase of treatment of kwashiorkor be increased from 4 to 8 mmol/kg/day.