In parts of the world where iodised salt is not routinely used, iodine deficiency in infants can be corrected by giving supplemental iodine either to breastfeeding mothers (indirect infant supplementation) or to the infants (direct infant supplementation). A randomized controlled trial from Morocco compared these two approaches. Mother-infant pairs were randomized to either receive one dose of 400 mg iodine to the mother and placebo to the infant, or one dose of 100 mg iodine to the infant and placebo to the mother. Compared to infants directly supplemented, infants in the indirect infant supplementation group had higher urinary iodine concentrations, and a lower frequency of thyroid hypofunction.There were no serious adverse events in either group. In geographic regions with iodine deficiency, providing breastfeeding women with a dose of 400 mg iodine immediately after delivery can ensure adequate iodine intake to the infants and potentially prevent hypothyroidism.