Under the Emergency Use Authorization issued in April 2009, oseltamivir can be used to treat 2009 influenza A (H1N1) virus infection in children aged <1 year. No data exist on the dosing of oseltamivir in premature babies. A hospital health care worker inadvertently exposed 32 neonatal intensive care unit babies to 2009 influenza A (H1N1); a protocol was expeditiously implemented to collect samples for pharmacokinetics and dosage evaluation. Results suggest 1.0 mg/kg/dose twice daily in premature babies produces oseltamivir carboxylate exposures similar to that in older children receiving 3.0 mg/kg/dose twice daily. These results provide initial guidance on dosing oseltamivir in this vulnerable population.