Briggs says "Diazepam may accumulate in breastfed infants, and its use in lactating women is not recommended. The American Academy of Pediatrics considers the effects of diazepam on the nursing infant to be unknown, but they may be of concern." You haven't said how old the infant is or what the dose of Valium is. Perhaps the dentist could prescribe something different if the mom REALLY NEEDS anything at all. Bonnie