The purpose of this study was to determine the applicability of two accepted outpatient management protocols for the febrile infant 1-2 months of age (Boston and Philadelphia protocols) in febrile infants 1-28 days of age. We retrospectively reviewed charts of patients 1-28 days of age with a temperature greater than or equal to 38.0 degrees C. Criteria from each of the above-cited management protocols were applied to the patients to determine their applicability in screening for serious bacterial infection (SBI). An SBI was defined as bacterial growth in cultures from blood, urine, cerebrospinal fluid (CSF), stool, or any aspirated fluid. Overall, 372 febrile infants were included in the study. Ages ranged from 1 to 28 days of age. The mean age was 15 days. SBI occurred in 45 patients (12%). The mean age of the patients with an SBI was 13 days. Thirty-two infants (8.6%) had a urinary tract infection; 12 (3.2%), bacteremia; five (1.3%), bacterial meningitis; three (0.8%), cellulitis; one (0.3%), septic arthritis; one (0.3%), bacterial gastroenteritis; and one (0.3%), pneumonia. Ten infants had more than one SBI. Of 372 patients, 231 (62%) met the Boston's laboratory low-risk criteria; eight (3.5%) would have been sent home with an SBI with these criteria. Philadelphia's laboratory low-risk criteria would have been met by 186 patients (50%); six (3.2%) would have been sent home with an SBI with these criteria. The negative predictive value of both the Boston and Philadelphia protocols for excluding an SBI was 97%. We conclude that current management protocols for febrile infants 1-2 months of age when applied to febrile infants 1 to 28 days of age would allow 3% of febrile infants less than 28 days of age to be sent home with an SBI. Current guidelines recommending admitting all febrile infants less than 28 days of age should be followed until the outcome of those 3% of febrile infants with an SBI treated as outpatients can be determined.