Uncomplicated malaria is defined as symptomatic malaria without signs of severity or evidence of vital organ dysfunction. In acute falciparum malaria there is a continuum from mild to severe malaria. Young children and non-immune adults with malaria may deteriorate rapidly. Detailed definitions of severe malaria are available (see section 8.1) to guide practitioners and for epidemiological and research purposes but, in practice, any patient whom the attending physician or health care worker suspects of having severe malaria should be treated as such initially. The risks of under-treating severe malaria considerably exceed those of giving parenteral or rectal treatment to a patient who does not need it.