The objective of this cross-sectional study was to identify risk factors for anemia among human immunodeficiency virus (HIV)-positive pregnant women in Dar es Salaam, Tanzania. Baseline data from 1064 women enrolled in a clinical trial on the effect of vitamin supplementation in HIV infection were examined to identify potential determinants of anemia. The mean hemoglobin (Hb) level was 94 g/L, and the prevalence of severe anemia (Hb < 85 g/L) was 28%; 83% of the women had Hb < 110 g/L. Iron deficiency and infectious disease appeared to be the predominant causes of anemia. Significant independent associations with severe anemia were observed for women with body mass index (BMI) < 19 kg/m(2) compared with women with BMI > 24 kg/m(2) [odds ratio (OR) 3.13, 95% confidence interval (CI): 1. 37-7.14); malaria parasite densities > 1000/mm(3) (OR 2.70, CI: 1. 58-4.61) compared with women with no parasites; eating soil during early pregnancy (OR 2.47, CI: 1.66-3.69); CD4+ cell count < 200/microL compared with CD4+ count > 500/microL (OR 2.70, CI: 1. 42-5.12); and serum retinol levels < 70 micromol/L (OR 2.45, CI: 1. 44-4.17) compared with women with retinol levels > 1.05 micromol/L. The most significant risk factors associated with severe anemia in this population are preventable. Public health recommendations include increasing the effectiveness of iron supplementation and malaria management during pregnancy, and providing health education messages that increase awareness of the potentially adverse nutritional consequences of eating soil during pregnancy.