BACKGROUND There is a potential for interaction between malaria and human immunodeficiency virus (HIV) infection. HIV infection might reduce immunity to malaria resulting in more frequent and severe infections; conversely malaria might enhance the progression of HIV infection to AIDS. In this paper we have reviewed some of the studies that have addressed this topic. METHODS Studies identified by a MEDLINE search were systematically reviewed and the measures of association between the two infections were either abstracted or recalculated from the reported data. Inferences drawn from these studies and the biological plausibility of an interaction are discussed. RESULTS The prevalence ratio (PR) of peripheral parasitaemia among HIV seropositive (HIVSP) individuals compared to HIV seronegative (HIVSN) individuals ranged from 0.72 to 0.94 in children and from 3.3 to 0.69 in adults. However, only one study showed a statistically significant difference between HIVSP and HIVSN groups (PR 3.3, 95% CI: 2.7-4.2). The rate ratio of non-severe malaria among HIVSP children compared to HIVSN children was 1.4 (95% CI: 0.99-2.0). Data from a trial of chemoprophylaxis during pregnancy suggested that placental malaria may predispose to perinatal transmission of HIV. Studies that have investigated the immune response to P. falciparum among HIVSP subjects have given variable results. CONCLUSIONS There is no convincing evidence for an interaction between malaria and HIV with the possible exception of an interaction between placental malaria and HIV infection. Several studies, however, had potentials for bias and/or an inadequate sample size. There is a need for carefully designed studies to resolve whether mortality from severe malaria, in particular cerebral malaria, is increased in HIVSP subjects, whether malaria infection of the placenta increases the risk of vertical transmission of HIV, and whether malaria infection increases the progression of HIV infection to AIDS.