Objective: This study evaluated the outcome of infants exposed to olanzapine during lactation. Methods: A prospective, controlled observational study design was used. Mothers who contacted Beilinson Teratology Information Service regarding use of olanzapine while breastfeeding were followed by phone interview. Data on lactation, neonatal symptoms, and outcome at the age of 1-2 years were obtained. Mother-infant groups were compared. Mothers breastfeeding while taking olanzapine (n = 22) were compared to two control groups of mothers who continued to take olanzapine but did not breastfeed (n = 15) and to breastfeeding mothers using a drug known to be safe during lactation (n = 51). Results: Follow-up was obtained for 37 of 70 women. Comparison of olanzapine-exposed breastfed versus control breastfed infants showed a similar duration of breastfeeding; however, early discontinuation of breastfeeding was more common in the olanzapine-exposed breastfed group (five of 22 vs. none of 51, p = 0.02). The rate of adverse outcomes in olanzapine-exposed breastfed infants did not differ from those of the control groups. Among the 30 newborns exposed in utero to olanzapine, no congenital birth defects were found. Neonatal symptoms were seen in six of 30 of olanzapine-exposed infants versus two of 51 of nonexposed infants (p < 0.05). A withdrawal syndrome was seen in three of 30 (10%) infants. Conclusions: No increase in adverse long-term outcomes in olanzapine-exposed breastfed infants were found. Our data in conjunction with previous estimates of very low drug exposure support continuation of breastfeeding in women treated with olanzapine. However, until additional long-term studies are available, infants exposed to olanzapine through breastmilk should be followed up.