The use of lithium salts in the treatment of affective neurosis has recently become popular. There have been no reports of neonatal lithium toxicity although it is embryopathic in other species. A newborn whose mother received lithium during the last month of pregnancy is presented. The infant manifested a 10-day course of cyanosis and lethargy with serum lithium levels in the adult toxic range. It is suggested lithium be used with caution during pregnancy.