The degree of immunity to malaria was estimated as follows: a) people who had been living in an endemic area for at least two years (emigrant) at the time of the diagnosis were presumed semi-immune, as well as adult migrant Africans that come to Portugal to visit friends or relatives; b) Europeans who travelled occasionally to endemic areas were considered non-immune. WHO's definition for severe malaria was applied and major and minor indicators considered according to the definitions presented in Table 1 . The number of severity criteria was quantified and analysed.