We report seven cases of naturally acquired human Plasmodium knowlesi infections which were admitted to our centre from July 2007 till June 2008. Diagnosis was confirmed by nested PCR. Cases of P. knowlesi infections, dubbed the fifth type of human malaria, have been reported in East Malaysia (Sabah and Sarawak) as well as in the state of Pahang in Peninsula Malaysia. These seven patients appear to be the first few reported cases of P. knowlesi infection in the Klang valley, Peninsula Malaysia. We then discuss the characteristics of human P. knowlesi infections, which include its natural hosts, responsible vectors, clinical presentation, and the treatment of such infections.