We describe the pharmacokinetics of raltegravir of a preterm newborn after short-course treatment of the mother tested HIV + the day of delivery. At age 1 month, the circulating concentration of raltegravir in the newborn was 29 ng/ml (the IC95 of RAL against HIV-1 is 15 ng/ml). Raltegravir should therefore be considered a potential transplacental postexposure prophylaxis for HIV-1 and an alternative to the use of boosted lopinavir in this context.