To describe the burden of malaria in Gauteng Province, and to identify potential risk factors for severe disease.We conducted a prospective survey of malaria cases diagnosed in hospitals throughout Gauteng from December 2005 to end November 2006.Malaria frequency, severity, and treatment. Results. We identified 1 701 malaria cases; 1 548 (91%) were seen at public sector hospitals and 153 (9%) at private hospitals; 1 149 (68%) patients were male. Median age was 27 years (range 1 month - 89 years). Most (84%) infections were acquired in Mozambique. Disease severity did not differ by age or sex. Patients who were South African-born were more likely to have severe disease (OR=1.43 (1.08 - 1.91)), as were patients who experienced a delay >48 hours between onset of symptoms and diagnosis or treatment (OR=1.98 (1.48 - 2.65)). While most patients appropriately received quinine, only 9% of severe malaria cases received the recommended loading dose.The incidence of malaria in Gauteng was higher than previously reported, emphasising the need to prevent malaria in travellers by correct use of non-drug measures and, when indicated, malaria chemoprophylaxis. Disease severity was increased by delays between onset and treatment and lack of partial immunity. Providers should consult the latest guidelines for treatment of malaria in South Africa, particularly about treatment of severe malaria. A change in drug policy to artemisinin combination therapy for imported uncomplicated malaria in non-malaria risk provinces should be strongly considered.