Authors report on a prospective study about malaria morbidity, carried out from April 1988 to March 1989. Malaria diagnosis was based on: 1. An unexplained fever, hours before, during or after entrance. 2. A parasitic density superior to 3,000 trophozoites per mm3 of blood. 3. Efficacy of parenteral malaria therapy. Among 480 hospitalized children, 20% suffered from a malaria attack; 44% of malaria attacks occurred within 6 and 23 months of age. Thus, malaria incidence seems considerable in this urban and lagoon environment. Malaria attacks were observed all year long but with unequal seasonal rates of incidence. As regards malaria morbidity studies, we propose that rates of incidence should be calculated according to several parasitic density thresholds so as to be able to compare various works.