To clarify the usefulness of oseltamivir in the elderly we administered oseltamivir to all residents when an influenza A outbreak occurred in a nursing home.Sixty-eight residents in the nursing home were investigated in which the influenza A outbreak occurred; 32 residents had fever and 28 residents were positive for influenza A with direct enzyme immunoassay.Oseltamivir was administered at 75 mg twice daily for 5 days to all residents.Oseltamivir almost inhibited symptom onset in the influenza A-positive afebrile group