Malaria must be included in the differential diagnosis of all febrile patients. Malaria is classified 'complicated' or 'uncomplicated', according to clinical findings (cerebral malaria, generalized convulsions, pulmonary edema, severe anemia, hyperthermia, renal failure, haemoglobinuria, shock, spontaneous bleeding) and laboratory results (parasitemia greater than 5%, haemoglobin less than 5 g%, creatinine greater than 265 mumol/l, glucose less than 2.2 mmol/l, DIC, pH less than 7.2, bilirubin greater than 50 mumol/l). Plasmodium (P.) vivax, P. ovale and P. malariae cause uncomplicated disease as a rule, whereas P. falciparum may result in either of both. Complicated falciparum malaria is always at risk for a lethal outcome. Only microscopic evidence of malaria parasites proofs the diagnosis. The thick smear is good for screening, thin films are necessary to determine the species. Serology and cultures are not helpful in diagnosing acute malaria. Tests for drug resistance await to be applicable for emergency situations.