Traditionally, psychiatric medications were withheld during pregnancy because of fear of teratogenic and other effects. The emergence of evidence of the safety of most commonly used psychiatric medications, the availability of this information in the form of online databases, and the documentation of the adverse effects of untreated maternal mental illness have all increased the comfort of physicians and patients with respect to the use of psychiatric medications during pregnancy. The tricyclic antidepressants and fluoxetine (Prozac) appear to be free of teratogenic effects, and emerging data support similar safety profiles for the other selective serotonin reuptake inhibitors. The mood stabilizers appear to be teratogenic. With the exception of the known risk for depression to worsen in the postpartum period, there is little consistent evidence of the effects of pregnancy on the natural history of mental illness. Decisions regarding the use of psychiatric medications should be individualized, and the most important factor is usually the patient's level of functioning in the past when she was not taking medications.