The Lithium Baby Register was founded in 1968 to determine the frequency of abnormalities among children born to mothers who were given lithium during the first trimester of pregnancy. Previous studies have revealed an increased frequency of congenital malformations, possibly due to teratogenic action of lithium. The present report is a questionnaire follow-up of the physical and mental development of lithium children who were not malformed at birth. Sixty lithium children were examined; their siblings, who had not been exposed to lithium during fetal life, served as a control group. The data obtained do not reveal any increased frequency of physical or mental anomalies among the lithium children.