We report an histological study from term placentas of 286 HIV positive women born in Rwanda. We observed chorioamnionitis without any pathogen in 15% of the cases, cocci Gram positive infection in 12 observations and malaria infection in 75% of placentas. We noted 71 cases of active malaria infection with Plasmodium falciparum trophozoites in the erythrocytes of the intervillous spaces, and 135 cases of chronic infection with malaria pigment without any parasite. An ultrastructural study performed in 8 cases of active malaria infection showed characteristic features of trophozoites and schizontes, and malaria pigment. No viral particle were seen. We did not observe any significative difference concerning the incidence of chorioamnionitis and of malaria infection in 275 HIV negative placentas. In the literature as well as in the present study, the main lesions observed in the placentas of AIDS patients were chorioamnionitis. Opportunistic infections and neoplasias of the placenta are exceptional. Detection of HIV proteins by immunochemistry or in situ hybridization is possible, but the HIV could not be identified in the trophoblast by electron microscopy. Mechanisms of the materno-fetal transmission for HIV are currently unknown.