The role of periconceptional folic acid supplementation in the prevention of neural tube defects (NTDs) has been well established. Maternal red blood cell (RBC) folate concentration is inversely associated with NTD risk, and concentrations above 906 nmol/L are associated with a low risk of NTDs. Current guidelines call for a minimum of 0.4 mg of folic acid per day for all women who could become pregnant and higher levels of supplementation for women with a family history of NTDs or risk factors associated with NTDs. However, there is variability in supplement adherence and lack of knowledge of conditions that may elevate folate requirements or NTD risk. Therefore, guidance provided to the population as a whole may be inappropriate for individual women. Current data show that a significant proportion of women of childbearing age have RBC folate concentrations below 906 nmol/L, rendering a higher-than-baseline risk for NTDs. Therapeutic drug monitoring (TDM) of RBC folate could be used to identify these women and to help them improve their folate status, thus reducing their risk for having a child with an NTD.This review describes the evolution of the evidence for TDM of RBC folate and preliminary experience with TDM in a population of 12 women who were planning a pregnancy and who were being treated with an atypical antipsychotic.