A simple decision analysis demonstrated elevated cost/utility ratio of rapid diagnostic testing (RDT) strategy at high malaria prevalence, in a hypothetical cohort of 100 febrile children. A. Decision analysis tree. Among simplifying assumptions (*), the cost of false negative malaria tests is neglected (given high test specificity and high disease prevalence). B. Equation relating the trade-off of increased cost but reduced number of unnecessary treatment courses associated with a strategy of RDT. C. Cost of two strategies (RDT, solid line versus presumptive treatment, dashed line) over a range of malaria prevalence. D. The cost of averting one unnecessary treatment with RDT rises steeply at high prevalence. NMFI, non-malaria febrile illness; TP, true positive; TN, true negative; FP, false positive; FN, false negative; cdx, cost of rapid diagnostic test; ctx, cost of treatment course; sens, sensitivity; spec, specificity; prev, prevalence.