Lithium therapy is currently a cornerstone of treatment for mothers who suffer bipolar disorders. Those who wish to breastfeed their children are often told they have to decide whether modifying the treatment for their disorder or even avoiding lactation. Lithium administration during breastfeeding has been described to produce certain side effects such as thyroid disorders, hypothermia and hypotonia. To our knowledge, there are few publications where infants have no laboratory abnormalities. Here we present the case of an infant without renal or thyroid alteration while he was breastfed.