(1) To obtain objective information about levetiracetam transplacental passage and its transport into colostrum, mature milk, and breastfed infants, we analyzed data from women treated for epilepsy between October 2006 and January 2021; (2) in this cohort study, maternal, umbilical cord, milk, and infant serum concentrations were measured at delivery, 2-4 days postpartum (colostrum) and 7-31 days postpartum (mature milk). Paired umbilical cord serum, maternal serum, breastfed infant serum, and milk concentrations were used to assess the ratios of umbilical cord/maternal serum, milk/maternal serum, and infant/maternal serum concentrations. The influence of combined treatment with enzyme-inducing antiseizure medication carbamazepine was assessed; (3) the umbilical cord/maternal serum concentration ratio ranged between 0.75 and 1.78 (mean 1.10 ± 0.33), paired maternal and umbilical cord serum concentrations were not significantly different, and a highly significant correlation was found between both concentrations. The mean milk/maternal serum concentration ratio was 1.14 ± 0.27 (2-4 days postpartum) and 1.04 ± 0.24 (7-31 days postpartum) while the mean infant/maternal serum concentration ratio was markedly lower (0.19 ± 0.13 and 0.14 ± 0.05, respectively); (4) levetiracetam was found in the umbilical cord at a concentration similar to those in maternal serum. All of the breastfed infant serum concentrations were below the reference range used for the general epileptic population.