During the last two decades it has been proved that free amoeba of the Naegleria and Acanthamoeba (Hartmanella) genera, formerly considered as inocuous protozoa, are the etiological agent of a newly described morbid entity: primary amoebic meningoencephalitis. The clinical aspects of this disease, its clinical and laboratory diagnosis, the pathogenic potential of these amoebae, epidemiological data, prophylaxis and treatment, have promoted medical interest in this disease and in the possibility of a differential diagnosis with other meningoencephalitides.