When large numbers of people are displaced within malaria endemic areas there is an increased risk of a malaria epidemic, especially when people living in an area with little or no malaria transmission move to an endemic area (e.g. displacement from highland to lowland areas). The lack of protective immunity, concentration of population, breakdown in public health activities and difficulties in accessing insecticides, insecticide-treated nets and effective treatment, all conspire to fuel epidemic malaria, in which morbidity and mortality are often high. Such circumstances are also ideal for the development of resistance to antimalarials. For these reasons, particular efforts must be made to deliver effective antimalarial treatment to the population at risk.