Treating mental disorders in pregnant or breastfeeding women is an important clinical issue. Antidepressant and antipsychotic drugs are generally considered to be relatively safe when used during pregnancy or breastfeeding. Benzodiazepine drugs, used for anxiety or insomnia, have a small but significant risk of birth defects. Antidepressant drugs could be used as an alternative for treating anxiety and insomnia. Lithium and anticonvulsant drugs (with the exception of lamotrigine) should generally be avoided during pregnancy. Antipsychotic drugs can be substituted for mood stabilizers. Use of anticonvulsant drugs is compatible with breastfeeding. Psychotherapy is a potential alternative to medication for the treatment of depression, anxiety disorders, and insomnia. Untreated maternal psychiatric illness can have adverse effects on pregnancy outcome and infant well-being. Available treatments and their potential risks when used during pregnancy or lactation should be discussed in the context of the risks of not treating maternal psychiatric illness effectively.