Morbidity monitoring will be carried out through a hospital/clinic based passive case detection system throughout the malaria transmission season from May to October. This will be complemented by one cross-sectional household survey at the end of the malaria transmission season in November during which interviews, haematological, parasitological and anthropometric assessments will be repeated. Children found to have severe anemia during the second survey will have a haematological work-up comprising Hb electrophoresis, full blood count, and stool examination. All study participants who visit the clinic will be treated by the health workers as usual in accordance with the current standard treatment guidelines in Ghana. In the case of mortality, at a culturally appropriate time, a trained field worker will visit the home and a standard questionnaire will be administered to the child's mother or caretaker. The results will be reviewed by three independent physicians to arrive at a possible diagnosis. If two out of three agree on a diagnosis of malaria, this diagnosis will be accepted. For children who visited hospital or died in the hospital, hospital case notes will be reviewed and where necessary, the attending physician will be interviewed for more complete information on the child's illness.