A retrospective study was performed of 292 infants younger than 2 months of age with a history of fever who received a standardized evaluation and were admitted to the hospital for possible sepsis. The purpose was to correlate the presence of this symptom with subsequent temperature patterns and the rate of serious bacterial infections (SBI). Caretakers reported fever per rectum via thermometer in 244 infants and tactile fever in 48 infants. Of 244 infants with reported fever per rectum, 224 (92%) had fever on presentation or during the subsequent 48 hours of hospitalization; by contrast, only 22 of 48 infants (46%) with reported tactile fever had fever on presentation or during the subsequent 48 hours of hospitalization (P less than 0.0001). Of 26 infants with tactile fever who were afebrile on presentation, none had subsequent fever during hospitalization and only 1 (3.8%) had SBI (urinary tract infection); of 40 infants with reported fever per rectum who were afebrile on presentation, 8 (20%) had subsequent fever during hospitalization and 4 (10%) had SBI (meningitis, bacteremia, osteomyelitis and urinary tract infection). There were a total of 19 infants (6.5%) with SBI; although 5 (27%) were afebrile on presentation (4 with reported fever per rectum, 1 with tactile fever), all 19 exhibited abnormal clinical and/or laboratory features on evaluation which were suggestive of underlying serious infection. Management decisions for young infants with reported fever should be based on both clinical findings and temperature-pattern profiles.