Pregnant women with low B12 levels are unable to provide the necessary amount of this vitamin to their fetuses. The mothers are usually not anemic, and failure to thrive and neurologic deficits are more common in their infants than in megaloblastic anemia. We report the case of a newborn that was born to a vegetarian mother and presented with the symptoms of megaloblastic anemia at birth; we also discuss vitamin B12 metabolism during pregnancy and lactation. An interesting feature of the present case is that it is the only reported case of a newborn that was treated by supplementation of the mother.