Transdermal testosterone gels are used in the treatment of hypoandrogenism of males. Virilization due to exposure to testosterone gels has been reported in children resulting in a US Food and Drug Administration (FDA) warning about secondary exposure to these products. At present, we are unaware of prenatal virilization associated with unintentional testosterone gel exposure. We report prenatal virilization in a female infant due to secondary maternal exposure to the father's testosterone gel. We also describe postnatal virilization of the child's twin sister.