We report a case of Plasmodium falciparum and Plasmodium malariae coinfection with associated failure of clinical response to artemether + lumefantrine therapy. This case highlights the need to consider co-infection in the setting of apparent treatment failure and the impact of mixed species infection upon host dynamics and clinical presentation. Recognition of malarial co-infection is clinically important for determining appropriate therapy and preventing disease sequelae. ? 2011 Elsevier Ltd. All rights reserved.