Infant iron status at birth is influenced by maternal iron status during pregnancy; however, there are limited data on the extent to which maternal iron status is associated with infant iron status during exclusive breastfeeding. We evaluated how maternal and infant hemoglobin and iron status [soluble transferrin receptors (TfR) and ferritin] were related during exclusive breastfeeding in HIV-infected women and their infants. The Breastfeeding, Antiretrovirals, and Nutrition Study was a randomized controlled trial in Lilongwe, Malawi, in which HIV-infected women were assigned with a 2 × 3 factorial design to a lipid-based nutrient supplement (LNS), or no LNS, and maternal, infant, or no antiretroviral drug, and followed for 24 wk. Longitudinal models were used to relate postpartum maternal hemoglobin (n = 1926) to concurrently measured infant hemoglobin, adjusting for initial infant hemoglobin values. In a subsample, change in infant iron status (hemoglobin, log ferritin, log TfR) between 2 (n = 352) or 6 wk (n = 167) and 24 wk (n = 519) was regressed on corresponding change in the maternal indicator, adjusting for 2 or 6 wk values. A 1 g/L higher maternal hemoglobin at 12, 18, and 24 wk was associated with a 0.06 g/L (P = 0.01), 0.10 g/L (P < 0.001), and 0.06 g/L (P = 0.01), respectively, higher infant hemoglobin. In the subsample, a reduction in maternal log TfR and an increase in hemoglobin from initial measurement to 24 wk were associated with the same pattern in infant values (log TfR β = -0.18 mg/L, P < 0.001; hemoglobin β = 0.13 g/L, P = 0.01). Given the observed influence of maternal and initial infant values, optimizing maternal iron status in pregnancy and postpartum is important to protect infant iron status. This trial was registered at clinicaltrials.gov as NCT00164736.