BACKGROUND: There is little information on the causes of low birth weight (LBW, <2500 g) in South Kivu. The authors determined the prevalence of LBW among full-term newborns, and its relationship with malaria and anaemia at the first antenatal visit (ANV1) in the rural health zone of Miti-Murhesa, in the eastern Democratic Republic of the Congo. METHODS: Four-hundred-and-seventy-eight pregnant women in the second trimester attending their first antenatal clinic were recruited between November 2010 and July 2011, and followed-up until delivery. Besides information on use of preventive measures and malaria morbidity, anthropometric measures and a blood sample were collected. RESULTS: Women's mean age (SD) at enrolment, was 26 (6.5) years (n=434); prevalence of malaria was 9.5% (43/453) and that of anaemia 32.2% (141/439). The latter was significantly more frequent in malaria-infected women and in those who had not been dewormed. At delivery, prevalence of LBW was 6.5% (23/355) and was independently associated with not sleeping under insecticide-treated bed net (p=0.030), mother's height <150 cm (p=0.001) and anaemia at the ANV1 (p=0.006). CONCLUSION: In South Kivu, malaria and anaemia are important risk factors for LBW, and should be prevented among all women of reproductive age.