The authors describe the first case of an isolated bilateral radial ray reduction occurring in a fetus exposed in utero to valproic acid; the diagnosis was made by ultrasound during the second trimester. This case of an isolated radial ray reduction associated with valproic acid use in pregnancy is a reminder for sonographers to carefully examine not only the cardiac and neurologic system, but also the extremities, when a fetus is exposed in utero to valproic acid.