Background: Typical treatment of moderate acute malnutrition, simple wasting, in sub-Saharan Africa consists of dietary counselling and/or general or targeted distribution of corn/soy-blended flour (CSB). A randomised clinical effectiveness trial in 2007 showed CSB to be less effective than ready-to-use supplementary food (RUSF). Aim: To determine the operational effectiveness of treating moderate acute malnutrition with RUSF. Methods: Children aged 6-59 months were recruited in rural southern Malawi. Each child received 65 kcal/kg/d of locally produced soy/peanut RUSF, a product that provided about 1 RDA of each micronutrient. Anthropometric measurements were taken every 2 weeks and additional rations of RUSF were distributed at this time if the child remained wasted. Study participation lasted up to 8 weeks. Results: Of the 2417 children enrolled, 80% recovered, 4% defaulted, 0.4% died, 12% remained moderately wasted and 3% developed severe acute malnutrition. Weight, length and MUAC gain were 2.6 g/kg/d, 0.2 mm/d and 0.1 mm/d respectively. Cost per child treated was $5.39. Conclusions: This intervention proved to be robust, maintaining high recovery rates and low default rates when instituted without the additional supervision and beneficiary incentives of a research setting.