With regard to an acute disease, Rift Valley fever, we tried to establish a prognostic score to help physicians to set prognosis and to choose a health management suitable in their context. Using clinical and biological data collected during the 1987 RVF epidemic in Southern Mauritania, we established a prognosis score card. Data analysis allows to prognosticate forms of possible severe evolution as an association of four syndromes: fever over 39 degrees, hemorrhagic syndrome, icterus and neurological signs. Using 12 clinical symptoms and 3 biological signs, it is possible to prognosticate cases with fatal evolution.