['In areas with intense malaria transmission, individuals are often simultaneously infected with multiple parasite strains. This study assessed the effect of multiple infections on treatment response in Ugandan children with uncomplicated malaria.', 'Four hundred and seventy six blood specimens were analysed for parasite genetic diversity. The P.falciparum merozoite surface protein-2 (msp-2) was analysed to establish multiplicity of infection for pre and post treatment specimens.', 'There were 32 different msp-2 alleles, 15 corresponding to the IC/3D7 and 17 to the FC27 allelic family. The majority of the isolates (343, 72 %) were multiple infections resulting into an overall mean multiplicity of infection of 2.15 (SD+/-1.02). Children infected with multiple strains had nearly a 3-fold increase in treatment failure (Hazard Ratio = 2.8, 95 % CI: 1.5-5.3) compared to their age mates infected with a single strain.'] Does multiplicity of Plasmodium falciparum infection predict antimalarial treatment outcome in Ugandan children?