A controlled clinical study compared the antipyretic effectiveness of acetaminophen administered at regular 4h intervals (group 1, n = 53) versus sporadic usage contingent upon a body temperature above 37.9 degrees C (group 2, n = 51) in 104 children presenting with simple febrile convulsions. The incidence of febrile episodes or temperature values were similar in spite of significantly larger amounts of acetaminophen administered to patients in group 1. Four and 4 children in groups 1 and 2, respectively, had a second episode of febrile seizures, in all of them within the first 24h of admission. We conclude that the prophylactic administration of acetaminophen in children with febrile seizures is not effective in the prevention of fever, the reduction of its degree, or in preventing the early recurrence of febrile seizures.