Neural tube defects are among the most common major congenital anomalies in the United States and may lead to a range of disabilities or death. Daily folic acid supplementation in the periconceptional period can prevent neural tube defects. However, most women do not receive the recommended daily intake of folate from diet alone. To update the 2009 US Preventive Services Task Force (USPSTF) recommendation on folic acid supplementation in women of childbearing age. In 2009, the USPSTF reviewed the effectiveness of folic acid supplementation in women of childbearing age for the prevention of neural tube defects in infants. The current review assessed new evidence on the benefits and harms of folic acid supplementation. The USPSTF assessed the balance of the benefits and harms of folic acid supplementation in women of childbearing age and determined that the net benefit is substantial. Evidence is adequate that the harms to the mother or infant from folic acid supplementation taken at the usual doses are no greater than small. Therefore, the USPSTF reaffirms its 2009 recommendation. The USPSTF recommends that all women who are planning or capable of pregnancy take a daily supplement containing 0.4 to 0.8 mg (400-800 µg) of folic acid. (A recommendation).