We have studied villages along the Thai-Myanmar border which are typical for the region and are classified by conventional epidemiological techniques as low-transmission (5-20% malaria prevalence). Our studies suggest that the majority of the population is infected. In Pailin, Western Cambodia, in areas where the National Malaria Control Programme and WHO believe that malaria has been all but eliminated, we have also found very high rates (>80%) of sub-microscopic parasitaemia in patients with fever or history of fever who are RDT negative. Thus, there is a lot more asymptomatic malaria in low transmission settings than previously thought, suggesting that control and elimination activities need to be rethought.